Porous material and method for recovering target substance using said porous material

Abstract

The purpose of the present invention is to provide a porous material having excellent adsorption performance and a method for recovering a target substance using the porous material. For achieving the purpose, provided is a porous material comprising: a porous body having a co-continuous structure configured of a ceramic framework (1) having mesopores (3) and of macropores (2); and sulfo groups with which the surfaces of the ceramic framework (1) are modified. The porous material has a content of sulfo groups of 0.7-5.0 mmol / g.

Description

Porous material and method for recovering target substances using said porous material

[0001] The present invention relates to a porous material and a method for recovering a target substance using the porous material.

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

[0003] International Publication No. 2017 / 002871

[0004] An object of the present invention is to provide a porous material having excellent adsorption performance and a method for recovering a target substance using the porous material.

[0005] The present inventors have discovered that in a porous material comprising a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and sulfo groups modifying the surface of the ceramic skeleton, the adsorption performance of the porous material can be improved by adjusting the amount of sulfo groups contained in the porous material to 0.7 mmol / g or more and 5.0 mmol / g or less, and have completed the present invention. That is, the present invention encompasses the following inventions.

[0006] [1] A porous material comprising a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and sulfo groups modifying the surface of the ceramic skeleton, wherein the amount of the sulfo groups contained in the porous material is 0.7 mmol / g or more and 5.0 mmol / g or less. [2] The porous material according to [1], wherein the amount of the sulfo groups is 3.6 mmol / g or more and 5.0 mmol / g or less. [3] The porous material according to [1] or [2], wherein the mode pore size of the macropores of the porous body is 200 nm or more and 5,000 nm or less. [4] The porous material according to any one of [1] to [3], wherein the ratio of the mode pore size of the macropores of the porous body to the mode pore size of the mesopores of the porous body is 15 or more and 300 or less. [5] The porous material according to any one of [1] to [4], wherein the ceramic skeleton of the porous body contains one or more elements selected from silicon, aluminum, tin, cerium, titanium, and zirconium. [6] A method for recovering one or more target substances selected from metals and their ions, and metalloids and their ions, from a solution containing the one or more target substances, the method comprising a step of contacting the solution with the porous material according to any one of [1] to [5]. [7] The method according to [6], wherein the one or more target substances are selected from transition elements including rare earth elements and their ions, and main group elements of Groups 1, 2, and 13 to 16 and their ions.

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

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

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

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

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

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

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

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

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

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

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

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

[0019] <Alkylene Group and Arylene Group> An alkylene group and an arylene group are divalent functional groups formed by removing one hydrogen atom from an alkyl group and an aryl group, respectively, and the alkyl group and the aryl group are described above.

[0020] <One or more substituents> The one or more substituents preferably mean 1 to 3 substituents, more preferably 1 or 2. The one or more substituents can be independently selected from, for example, a hydroxyl group, a carboxyl group, a halogen atom, a phosphate group, an oxo group, an alkyloxy group, an aryloxy group, an arylalkyloxy group, an alkylaryloxy group, and the like.

[0021] <<Porous Body>> The porous body has a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores. Hereinafter, the porous body will be described.

[0022] <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.

[0023] 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.

[0024] 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.

[0025] <Structure of Porous Body Before Modification> Hereinafter, the structure of the porous body before modification with sulfo groups will be described with reference to FIG.

[0026] As shown in FIG. 1, the porous body has a bicontinuous structure formed by a ceramic skeleton 1 containing mesopores 3 and macropores 2 .

[0027] 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. The fact that the porous body has a co-continuous structure can be confirmed by observing the surface or cross section of the porous body with a scanning electron microscope (SEM).

[0028] From the viewpoint of improving the adsorption performance, the mode pore diameter of the macropores 2 is preferably 200 nm or more, more preferably 400 nm or more, and even more preferably 600 nm or more. From the same viewpoint, the mode pore diameter of the macropores 2 is preferably 5000 nm or less, more preferably 4500 nm or less, even more preferably 4000 nm or less, and even more preferably 3000 nm or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0029] 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.

[0030] From the viewpoint of improving adsorption performance, the mode pore diameter of the mesopores 3 is preferably 2.0 nm or more, more preferably 5.0 nm or more, and even more preferably 10.0 nm or more. From the same viewpoint, the mode pore diameter of the mesopores 3 is preferably 50.0 nm or less, more preferably 40.0 nm or less, and even more preferably 35.0 nm or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0031] 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.

[0032] From the viewpoint of improving the adsorption performance, the ratio of the most frequent pore size of the macropores 2 to the most frequent pore size of the mesopores 3 is preferably 15 or more, more preferably 20 or more, even more preferably 30 or more, and still more preferably 40 or more. From the same viewpoint, the ratio is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less, and still more preferably 100 or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0033] From the viewpoint of improving the adsorption performance, the specific surface area of ​​the porous body measured by the BET method from the nitrogen adsorption / desorption isotherm is preferably 100 m ２ / g or more, more preferably 120m ２ / g or more, more preferably 130m ２ The upper limit of the specific surface area of ​​the porous body is not particularly limited, but is typically 800 m ２ The method for measuring the specific surface area by the BET method from the nitrogen adsorption / desorption isotherm is as described in the examples below.

[0034] From the viewpoint of improving the adsorption performance, the total pore volume of the porous body measured by mercury porosimetry is preferably 1.5 mL / g or more and 4.0 mL / g or less, more preferably 1.8 mL / g or more and 3.5 mL / g or less, and even more preferably 2.5 mL / g or more and 3.5 mL / g or less. The method for measuring the total pore volume by mercury porosimetry is as described in the Examples below.

[0035] From the viewpoint of improving the adsorption performance, the porosity of the porous body measured by mercury porosimetry is preferably 70% or more and 90% or less, more preferably 70% or more and 85% or less, and even more preferably 75% or more and 85% or less. The method for measuring the porosity by mercury porosimetry is as described in the Examples below.

[0036] <Material of Porous Body> The ceramics constituting the ceramic skeleton are, for example, oxide ceramics containing a metalloid element or a metal element. The ceramic skeleton 1 may contain one element selected from the group consisting of metalloid elements and metal elements, or may contain two or more elements selected from the group consisting of metalloid elements and metal elements.

[0037] An example of a semi-metallic element is silicon. An example of an oxide ceramic containing silicon is silica (SiO ２ ) are listed.

[0038] Examples of the metal element include aluminum, tin, and transition metal elements such as cerium, titanium, zirconium, vanadium, chromium, iron, cobalt, nickel, palladium, platinum, copper, silver, gold, and zinc. Among these, from the viewpoint of ease of manufacturing the porous body, the metal element is preferably selected from aluminum, tin, cerium, titanium, and zirconium. Examples of oxide ceramics containing aluminum, tin, cerium, titanium, or zirconium include alumina (Al ２ O ３ ), tin oxide (SnO ２ ), ceria (CeO ２ ), titania (TiO ２ ), zirconia (ZrO ２ ) etc.

[0039] The oxide ceramic may further contain, in addition to silicon, aluminum, tin or a transition metal element, an element selected from alkali metal elements such as lithium and sodium, alkaline earth metal elements such as magnesium and calcium, and rare earth elements such as lanthanum, scandium, yttrium and gadolinium.

[0040] <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).

[0041] 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.

[0042] 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.

[0043] The produced ceramic monolith may be molded and used as a porous body, or a molded ceramic monolith may be produced using a mold or the like and used as is or after further molding as needed as a porous body. For example, a molded ceramic monolith can be produced by using a molding mold to mold the 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.

[0044] The produced ceramic monolith may be pulverized and used as a porous body. Pulverization can be carried out according to a conventional method. Pulverization can be carried out using, for example, a mortar, a hammer mill, a ball mill, a bead mill, a jet mill, a roller mill, or the like. The particle diameter of the porous body after pulverization is preferably 0.5 μm or more and 7.0 mm or less, more preferably 2.0 μm or more and 5.0 mm or less, and even more preferably 5.0 μm or more and 3.0 mm or less. Note that "particle diameter" refers to the circle-equivalent diameter, that is, the diameter of a circle when a circle having an area equal to the area of ​​the porous body after pulverization is assumed in an observation image (e.g., an SEM image) of the porous body after pulverization.

[0045] The porous material of the present invention comprises a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and a sulfo group modifying the surface of the ceramic skeleton. The sulfo group is represented by the formula: -SO ３ It is a monovalent group represented by H. The porous material of the present invention will be described below.

[0046] <Surface Modification> The surface of the ceramic skeleton is modified with a sulfo group. The surface of the ceramic skeleton may be modified only with a sulfo group, or may be modified with a sulfo group and one or more functional groups other than a sulfo group. The sulfo group may be bonded directly to the surface of the ceramic skeleton, or may be bonded to the surface of the ceramic skeleton via a linker.

[0047] The surface of the ceramic skeleton includes the inner and outer surfaces of the ceramic skeleton. The inner surface of the ceramic skeleton includes the inner surfaces of the macropores and mesopores present inside the ceramic skeleton (i.e., not exposed on the outer surface of the ceramic skeleton), and the outer surface of the ceramic skeleton includes the inner surfaces of the macropores and mesopores exposed on the outer surface of the ceramic skeleton. Of the surfaces of the ceramic skeleton, at least the inner surface is preferably modified with a sulfo group.

[0048] In one embodiment, a compound having a sulfo group (hereinafter referred to as the "first compound") is fixed to the surface of the ceramic skeleton, thereby modifying the surface of the ceramic skeleton with the sulfo group. Methods for introducing the first compound to the surface of the ceramic skeleton include, for example, a method for chemically fixing the first compound to the surface of the ceramic skeleton via a covalent bond, and a method for physically fixing the first compound to the surface of the ceramic skeleton via a physical interaction such as an ionic bond or a hydrophobic interaction. A method for chemically introducing the first compound to the surface of the ceramic skeleton includes, for example, a method for reacting the first compound with a functional group (e.g., a hydroxyl group) on the surface of the ceramic skeleton to chemically fix the first compound to the surface of the ceramic skeleton. The first compound may be fixed to the surface of the ceramic skeleton via a linker. For example, a functional group reactive with the first compound may be introduced to the surface of the ceramic skeleton, and then the introduced functional group may be reacted with the first compound to chemically fix the first compound to the surface of the ceramic skeleton. A method for introducing a functional group that reacts with the first compound onto the surface of a ceramic skeleton includes reacting a functional group (e.g., a hydroxyl group) on the surface of the ceramic skeleton with a silane coupling agent having a functional group that reacts with the first compound, and chemically fixing the silane coupling agent to the surface of the ceramic skeleton. Examples of silane coupling agents having a functional group that reacts with the first compound include silane coupling agents having an epoxy group and / or a haloalkyl group. Examples of silane coupling agents having an epoxy group include 3-glycidyloxypropyltrimethoxysilane. Examples of silane coupling agents having a haloalkyl group include 3-chloropropyltrimethoxysilane.

[0049] A method for modifying the surface of a ceramic skeleton with a sulfo group may involve immobilizing a compound containing a thiol group (—SH) (hereinafter referred to as the “second compound”) on the surface of the ceramic skeleton, and then converting the thiol group contained in the second compound to a sulfo group. The second compound can be immobilized on the surface of the ceramic skeleton in the same manner as the first compound. The conversion of the thiol group to a sulfo group can be carried out according to a conventional method. Even if the compound immobilized on 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 immobilizing a compound having a sulfo group on the surface of the ceramic skeleton.”

[0050] 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.

[0051] The sulfo groups introduced onto the surface of the ceramic skeleton are preferably fixed to the surface of the ceramic skeleton via a linker such as a silane coupling agent. When the linker is, for example, a silane coupling agent, the carbon skeleton of the silane coupling agent allows the sulfo groups to move flexibly while fixed to the surface of the ceramic skeleton. This makes it easier for each sulfo group to act on the target substance, and multiple sulfo groups work together to act on the target substance, resulting in higher adsorption performance than when sulfo groups are directly introduced onto the surface of the ceramic skeleton.

[0052] Examples of the silane coupling agent containing a sulfo group include silane coupling agents represented by Formula A or B. Formula A: R ａ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula B: R ａ -R ｄ -Si(-O-(R ｅ -O) ｍ -R ｆ ) ｎ (-R ｃ ) ３－ｎ

[0053] Examples of silane coupling agents containing a thiol group include silane coupling agents represented by formula C or D. Formula C:R ｇ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula D:R ｇ -R ｄ -Si(-O-(R ｅ -O) ｍ -R ｆ ) ｎ (-R ｃ ) ３－ｎ

[0054] In Formula A, R ａ represents a sulfo group, and R ｂ each independently represents an alkyl group, R ｃ each independently represents an alkyloxy group or a halogen atom, R ｄ represents an alkylene group, an arylene group, or a combination thereof; and n represents an integer of 0 to 2.

[0055] In Formula B, R ａ , R ｃ , R ｄ and n are as defined in formula A, and R ｅ each independently represents an alkylene group; R ｆ each independently represents an alkyl group, and m represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably an integer of 1 or 2.

[0056] In Formula C, R ｂ , R ｃ , R ｄ and n are as defined in formula A, and R ｇ represents a thiol group.

[0057] In Formula D, R ｃ , R ｄ and n are as defined in formula A, and R ｅ , R ｆ and m are as defined in formula B, and R ｇ is synonymous with formula C.

[0058] R ｂ or R ｆ Examples of the alkyl group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0059] R ｃ Examples of the alkyloxy group or halogen atom represented by R include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a chlorine atom, a bromine atom, and an iodine atom. ｃ The alkyloxy group represented by R is preferably a methoxy group or an ethoxy group. ｃ The halogen group represented by the formula (I) is preferably a chlorine atom.

[0060] R ｄ or R ｅ Examples of the alkylene group represented by the formula (I) include a methylene group, an ethylene group, a propylene group, and a butylene group.

[0061] R ｄ Examples of the arylene group represented by the formula (I) include a phenylene group, a naphthylene group, and a biphenylene group.

[0062] R ｄ Examples of the combination of an alkylene group and an arylene group represented by the formula include groups represented by the formula: -X-Y-, -Y-X-, -X-Y-X-, or -Y-X-Y-, where X represents an alkylene group and Y represents an arylene group.

[0063] R ｄ The alkylene group, arylene group, or combination thereof represented by the formula (I) may have one or more substituents.

[0064] Examples of the silane coupling agent represented by formula A include 3-(trimethoxysilyl)-1-propanesulfonic acid.

[0065] Examples of the silane coupling agent represented by formula B include 3-(dimethoxy(2-methoxyethoxy)silyl)-1-propanesulfonic acid.

[0066] Examples of the silane coupling agent represented by formula C include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltriethoxysilane.

[0067] Examples of the silane coupling agent represented by formula D include ethoxy(3-mercaptopropyl)bis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silane.

[0068] The greater the amount of sulfo groups introduced onto the surface of the ceramic skeleton, the better the adsorption performance. Therefore, from the perspective of effectively improving the adsorption performance of the porous material, the amount of sulfo groups contained in the porous material is 0.7 mmol / g or more, preferably 1.0 mmol / g or more, more preferably 1.3 mmol / g or more, even more preferably 1.7 mmol / g or more, and even more preferably 3.6 mmol / g or more, based on the mass of the porous material. However, when sulfo groups are introduced via a linker, as the amount of sulfo groups introduced onto the surface of the ceramic skeleton increases, the amount of hydrocarbon groups (e.g., alkyl groups, alkylene groups, arylene groups, etc.) contained in the compound introduced as the linker, such as a silane coupling agent, also increases, thereby increasing the hydrophobicity of the porous material. When the hydrophobicity of the porous material increases, it becomes difficult for the solution containing the target substance to reach the pores, and the sulfo groups introduced onto the surface of the ceramic skeleton cannot be effectively utilized, resulting in a decrease in adsorption performance. Furthermore, when sulfo groups are introduced directly onto the surface of the ceramic skeleton, the amount of sulfo groups introduced is affected by the skeletal structure of the porous material, so there is an upper limit. Therefore, from the viewpoint of effectively improving the adsorption performance of the porous material, the amount of sulfo groups contained in the porous material is 5.0 mmol / g or less, preferably 4.5 mmol / g or less, and more preferably 4.0 mmol / g or less, based on the mass of the porous material. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0069] The above ranges for the amount of sulfo groups contained in the porous material are mainly applied when the porous material is used as an adsorbent. For example, when the porous material is used as an ion exchange material, the amount of sulfo groups contained in the porous material may be adjusted to fall within the above ranges or outside the above ranges.

[0070] The "amount of sulfo groups" refers to the amount of sulfur atoms derived from sulfo groups contained in the porous material. When all sulfur atoms contained in the porous material are sulfo atoms derived from sulfo groups, the "amount of sulfo groups" refers to the amount of all sulfur atoms contained in the porous material. 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.

[0071] <Method for producing porous material> In one embodiment, the porous material of the present invention can be produced by a method comprising the following steps: (1) modifying the surface of a ceramic skeleton of a porous body with thiol groups; and (2) converting the thiol groups to sulfo groups. This method is advantageous in that it makes it easy to adjust the amount of sulfo groups contained in the porous material.

[0072] Step (1) 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.

[0073] 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 C or D can be used.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 (2).

[0079] Step (2) can be carried out by contacting the thiol group-modified porous material obtained in step (1) with a reagent for converting the thiol group to a sulfo group (hereinafter referred to as the "second reagent") in a second solvent.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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 porous material of the present invention can be obtained.

[0084] In another embodiment, the porous material of the present invention can be produced by a method including a step of directly modifying the surface of a ceramic skeleton of a 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 a porous body can be directly modified with sulfo groups by adding chlorosulfonic acid to the porous body and stirring the mixture.

[0085] <Applications> The porous material of the present invention can be used in applications that utilize the function of the sulfo group.

[0086] In one embodiment, the porous material of the present invention can be used as an ion exchange material.

[0087] The sulfo group can adsorb one or more target substances selected from the group consisting of metals and their ions, and metalloids and their ions. Therefore, in one embodiment, the porous material of the present invention is useful as an adsorbent for adsorbing one or more target substances selected from the above group, and can be used to recover one or more target substances selected from the above group.

[0088] Examples of metals and their ions and metalloids and their ions include transition elements and their ions, and typical elements of Groups 1, 2, and 13 to 16 and their ions.

[0089] Transition elements 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 elements.

[0090] Rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0091] Typical elements of Groups 1, 2, and 13 to 16 include Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, 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 semimetals.

[0092] The sulfo group has particularly high adsorption capacity for Co, Fe, and Ni among transition elements, for Y and La among rare earth elements, and for Sr and Zn among typical elements. Therefore, the porous material of the present invention is particularly useful as an adsorbent for adsorbing one or more target substances selected from these elements.

[0093] Examples of the form of metals and metalloids adsorbed to the sulfo group include metal nanoparticles and metalloid nanoparticles. The metals and ions thereof, and the metalloids and ions thereof adsorbed to the sulfo group may or may not have ligands.

[0094] <<Method for recovering target substance>> The method for recovering target substance of the present invention is a method for recovering one or more target substances from a solution (hereinafter referred to as "liquid to be treated") containing one or more target substances selected from metals and their ions, and metalloids and their ions, and includes a step of contacting the liquid to be treated with the porous material of the present invention.

[0095] When a liquid to be treated is brought into contact with the porous material of the present invention, one or more target substances contained in the liquid to be treated are adsorbed by the porous material of the present invention, thereby making it possible to recover one or more target substances from the liquid to be treated.

[0096] Examples of the liquid to be treated include wastewater discharged from a plant or the like, and wastewater containing valuable metals discharged from a metal refining process. The liquid to be treated usually contains water. The wastewater or wastewater may be pretreated as necessary before being brought into contact with the porous material of the present invention.

[0097] The one or more target substances contained in the liquid to be treated can be selected from, for example, transition metals including rare earth metals and their ions, and typical elements of Groups 1, 2, and 13 to 16 and their ions. The sulfo group has particularly high adsorption capacity for Co, Fe, and Ni among the transition elements, Y and La among the rare earth elements, and Sr and Zn among the typical elements. Therefore, it is preferable that the one or more target substances contained in the liquid to be treated be selected from these elements.

[0098] Examples of methods for contacting the liquid to be treated with the porous material of the present invention include a method of immersing the porous material of the present invention in the liquid to be treated, a method of passing the liquid to be treated through a column packed with the porous material of the present invention, etc. The liquid can be passed through, for example, using a liquid feed pump.

[0099] The porous material of the present invention is particularly useful when recovering target substances from a liquid to be treated in which the concentration of each target substance is low (for example, the concentration of each target substance is 0.1 ppm or more and 5000 ppm or less, particularly 0.1 ppm or more and 100 ppm or less).

[0100] The present invention will be explained in more detail below based on examples and comparative examples, but the scope of the present invention is not limited by these examples and comparative examples.

[0101] Example 1 (1) Preparation of Silica Monolith 8.67 g of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH), 7.80 g of urea, and 86.7 g of an aqueous acetic acid solution (acetic acid concentration: 6.06% by mass) were added to a 150 mL reaction vessel and stirred at room temperature for 10 minutes. The reaction vessel was placed in an ice bath, and the reaction solution was cooled with stirring for 15 minutes. 44.7 g of tetramethoxysilane was added to the cooled reaction solution, and the mixture was stirred for 30 minutes while cooling in the ice bath. The reaction solution was heated in a 30°C warm bath and then left to stand overnight in an incubator at 30°C to prepare a polysiloxane gel.

[0102] The resulting polysiloxane gel was then added to a separate reaction vessel containing 30 mL of 3 mol / L urea water, and the mixture was heated under reflux for 12 hours. After the reaction was completed, the resulting polysiloxane gel was washed with water and dried for 12 hours in a dryer set at 60°C. After drying, the gel was fired at 600°C for 5 hours in an air atmosphere to produce a silica monolith. The produced silica monolith was pulverized and classified to obtain a silica monolith with a particle size of 100 μm or more and 300 μm or less.

[0103] (2) Observation by Scanning Electron Microscope (SEM) The surface structure of the silica monolith obtained in (1) above was observed by SEM (JSM-7900F manufactured by JEOL), and it was confirmed that the silica monolith had a bicontinuous structure formed by a silica skeleton and macropores.

[0104] (3) Measurement of specific surface area and most frequent pore size of mesopores The specific surface area and most frequent pore size of mesopores of the silica monolith obtained in (1) above were measured using a specific surface area and pore size distribution measuring device (BELSORP-miniX manufactured by Microtrac-Bell). For a silica monolith that had been degassed under reduced pressure at 400°C for 3 hours, the amount of nitrogen adsorption and desorption at a temperature of 77K was measured using liquid nitrogen by a multipoint method to obtain an adsorption and desorption isotherm, and the specific surface area and most frequent pore size were calculated based on the adsorption and desorption isotherm. The specific surface area was calculated by the BET method, and the most frequent pore size was calculated by the BJH method.

[0105] 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.

[0106] (4) Measurement of total pore volume, most frequent pore size of macropores, and porosity The total pore volume, most frequent pore size of macropores, and porosity of the silica monolith obtained in (1) above were measured by mercury intrusion porosimetry using a mercury porosimeter (AutoPore IV 9520 manufactured by Micromeritics). In mercury intrusion porosimetry, pressure was applied to the pores of the silica monolith to infiltrate mercury, and the pore volume and specific surface area were determined from the pressure and the amount of mercury intruded. The pore diameter was calculated from the relationship between the pore volume and the specific surface area when the pores were assumed to be cylindrical. In the present invention, mercury intrusion porosimetry was used to analyze a range of pores having a diameter of 50 nm to 500 μm. The measurement was performed under the following conditions and procedures.

[0107] (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

[0108] (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.

[0109] The results of (3) and (4) above are shown in Table 1.

[0110]

[0111] (5) Preparation of thiol group-modified silica monolith 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 (1) above were added to a reaction vessel, and the mixture was left to stand at room temperature for 30 minutes, and then heated 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.

[0112] (6) Preparation of sulfo group-modified silica monolith 3.0 g of the thiol group-modified silica monolith obtained in (5) above, 15 mL of hydrogen peroxide solution (hydrogen peroxide concentration: 30 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 preparing 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.

[0113] (7) Measurement of sulfo group amount The amount of sulfur atoms contained in the sulfo group-modified silica monolith obtained in (6) above 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 results are shown in Table 2.

[0114] (8) Metal Adsorption Test by Solution Immersion 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Co concentration: 100 ppm, pH: 2) prepared by diluting a cobalt standard solution (Co1000, manufactured by Kanto Chemical Co., Inc.) 10 times with pure water, and the mixture was stirred at 400 rpm for 30 minutes at 25 °C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amount of Co contained in the resulting filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of Co adsorbed on the sulfo-modified silica monolith relative to the amount of Co initially contained in the aqueous solution (hereinafter referred to as the "Co adsorption rate") was calculated. The Co adsorption rates are shown in Table 2.

[0115] 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Fe concentration: 100 ppm, pH: 2) prepared by diluting an iron standard solution (Fe1000, manufactured by Kanto Chemical Co., Ltd.) 10 times with pure water, and the mixture was stirred at 400 rpm for 30 minutes at 25°C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amount of Fe contained in the resulting filtrate was analyzed using an ICP emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of Fe adsorbed to the sulfo-modified silica monolith relative to the amount of Fe initially contained in the aqueous solution (hereinafter referred to as the "Fe adsorption rate") was calculated. The Fe adsorption rate is shown in Table 2.

[0116] 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Zn concentration: 100 ppm, pH: 2) prepared by diluting a zinc standard solution (Zn1000, manufactured by Kanto Chemical Co., Ltd.) 10 times with pure water, and the mixture was stirred at 400 rpm for 30 minutes at 25°C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amount of Zn contained in the resulting filtrate was analyzed using an ICP emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of Zn adsorbed to the sulfo-modified silica monolith relative to the amount of Zn initially contained in the aqueous solution (hereinafter referred to as the "Zn adsorption rate") was calculated. The Zn adsorption rates are shown in Table 2.

[0117] 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Ni concentration: 100 ppm, pH: 2) prepared by diluting a nickel standard solution (Ni1000, manufactured by Kanto Chemical Co., Ltd.) 10 times with pure water, and the mixture was stirred at 400 rpm for 30 minutes at 25°C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amount of Ni contained in the obtained filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of Ni element adsorbed on the sulfo-modified silica monolith relative to the amount of Ni element initially contained in the aqueous solution (hereinafter referred to as the "Ni adsorption rate") was calculated. The Ni adsorption rate is shown in Table 2.

[0118] 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Sr concentration: 100 ppm, pH: 2) prepared by diluting a strontium standard solution (Sr1000, manufactured by Kanto Chemical Co., Ltd.) 10 times with pure water, and the mixture was stirred at 400 rpm for 30 minutes at 25°C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amount of Sr contained in the obtained filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of Sr element adsorbed on the sulfo-modified silica monolith relative to the amount of Sr element initially contained in the aqueous solution (hereinafter referred to as the "Sr adsorption rate") was calculated. The Sr adsorption rate is shown in Table 2.

[0119] 120 mg of the sulfo-modified silica monolith obtained in (6) above was immersed in 30 mL of an aqueous solution (Fe and Pd concentrations: 100 ppm, pH: 2) prepared by diluting an iron standard solution (Fe1000, manufactured by Kanto Chemical Co., Ltd.) and a palladium standard solution (Pd1000, manufactured by Kanto Chemical Co., Ltd.) 10 times with pure water and then adjusting the pH to 2 with sodium carbonate. The mixture was stirred at 400 rpm for 30 minutes at 25°C. After the reaction was completed, the sulfo-modified silica monolith was separated by filtration, and the amounts of Fe and Pd contained in the obtained filtrate were analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The Fe selectivity calculated according to the following formula is shown in Table 2. Fe selectivity = (amount of Fe adsorbed on the sulfo-modified silica monolith) / (total amount of Fe and Pd adsorbed on the sulfo-modified silica monolith).

[0120]

[0121] In addition, in the sulfo group-modified silica monolith of the present invention, if the Fe selectivity is 0.7 or more, it can be determined that no thiol groups remain in the sulfo group-modified silica monolith (i.e., the thiol groups contained in the thiol group-modified silica monolith have been completely converted to sulfo groups).

[0122] [Example 2] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 3.06 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0123] [Example 3] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 4.08 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0124] [Example 4] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 5.11 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0125] [Example 5] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 6.13 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0126] [Example 6] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 16.4 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0127] [Example 7] A sulfo group-modified silica monolith was produced and evaluated in the same manner as in Example 1, except that the amount of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH) used was changed to 9.97 g in the production of the silica monolith. The results are shown in Tables 1 and 2. It was confirmed by SEM observation in the same manner as in Example 1 that the produced silica monolith had a co-continuous structure.

[0128] [Example 8] A sulfo group-modified silica monolith was produced and evaluated in the same manner as in Example 1, except that the amount of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH) used was changed to 7.08 g in the production of the silica monolith. The results are shown in Tables 1 and 2. It was confirmed by SEM observation in the same manner as in Example 1 that the produced silica monolith had a co-continuous structure.

[0129] [Example 9] A sulfo group-modified silica monolith was produced and evaluated in the same manner as in Example 1, except that the heating reflux time in 3 mol / L urea water was changed to 5 hours in the production of the silica monolith. The results are shown in Tables 1 and 2. The fact that the produced silica monolith had a co-continuous structure was confirmed by SEM observation in the same manner as in Example 1.

[0130] [Example 10] A sulfo group-modified silica monolith was produced and evaluated in the same manner as in Example 1, except that the heating reflux time in 3 mol / L urea water was changed to 24 hours in the production of the silica monolith. The results are shown in Tables 1 and 2. The fact that the produced silica monolith had a co-continuous structure was confirmed by SEM observation in the same manner as in Example 1.

[0131] [Comparative Example 1] In the preparation of the thiol group-modified silica monolith, except that the amount of 3-mercaptopropyltrimethoxysilane used was changed to 1.02 g, a sulfo group-modified silica monolith was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0132] Comparative Example 2 The same evaluation as in Example 1 was carried out using commercially available sulfo-modified silica (manufactured by Aldrich). The results are shown in Table 2. The commercially available sulfo-modified silica used did not have a co-continuous structure. The specific surface area, most frequent macropore diameter, most frequent mesopore diameter, total pore volume, and porosity were not measured, and therefore are indicated as "-" in Table 1.

[0133] [Comparative Example 3] A thiol group-modified silica monolith was prepared in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in the preparation of the thiol group-modified silica monolith was changed to 4.08 g, and the prepared thiol group-modified silica monolith was used to carry out the same evaluation as in Example 1. The results are shown in Tables 1 and 2.

[0134] 1...Ceramic skeleton 2...Macropores 3...Mesopores

Claims

1. A porous material comprising a porous body having a bicontinuous structure formed by a ceramic skeleton including mesopores and macropores, and sulfo groups modifying the surface of the ceramic skeleton, wherein the amount of the sulfo groups contained in the porous material is 0.7 mmol / g or more and 5.0 mmol / g or less.

2. The porous material according to claim 1, wherein the amount of the sulfo group is 3.6 mmol / g or more and 5.0 mmol / g or less.

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

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

5. The porous material according to claim 1 or 2, wherein the ceramic skeleton of the porous body contains one or more elements selected from the group consisting of silicon, aluminum, tin, cerium, titanium and zirconium.

6. A method for recovering one or more target substances selected from metals and their ions, and metalloids and their ions, from a solution containing the one or more target substances, the method comprising a step of contacting the solution with the porous material described in claim 1 or 2.

7. The method of claim 6, wherein the one or more target substances are selected from transition elements and ions thereof, including rare earth elements, and main group elements and ions thereof of Groups 1, 2, and 13-16.

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