JP6099040B2 - Composite layered double hydroxide - Google Patents

Description

The present invention relates to a composite layered double hydroxide. More specifically, the present invention relates to a composite layered double hydroxide that can be suitably used as an anion exchanger and is expected to be used as an anion conductive electrolyte membrane material and a catalyst material for secondary batteries and fuel cells.

Layered double hydroxides (LDH) ^is a _{^{M 2+ 1-x L 3+ x}} (OH) non-stoichiometric compound represented by the general formula _{2 A n- x / n · yH} 2 O, clay mineral similarly layered has a ^structure, by M 2+ _{(OH) 6} octahedral layer (brucite layers) ^{M 2+} in is isomorphous replacement to ^{L 3+,} have a positive charge, in order to compensate for this positive charge, the LDH Anions (A ⁿ⁻ ) are coordinated between the layers.
Since LDH has characteristics such as basicity, anion exchange ability, and low toxicity, it is used as a CO ₂ adsorbent, catalyst, catalyst carrier, drug carrier, anion conductor, nanocomposite host material, and the like. In particular, LDH is expected to be an effective material for removing harmful metals contained in the form of oxoanions in water because of its high anion exchange ability. However, LDH has an extremely high affinity with carbonate ions (CO ₃ ²⁻ ), and has the property of selectively incorporating carbonate ions as interlayer anions by anion exchange reaction. There is a problem that it must be carried out under the condition that no carbon dioxide (CO ₂ ) is present.

Various efforts have been made to improve the above problems.
The anion possessed by LDH is closer to the end of the interlayer (near the surface of the LDH particle) than the one located closer to the interior of the interlayer (inside the LDH particle). Expected to occur easily. Therefore, as one approach to the above problem, the amount of anion exchange sites located in the vicinity of the end portions between layers is increased by suppressing crystal growth during synthesis of LDH particles and making LDH fine particles (nanoparticles). Efforts have been made (Non-Patent Documents 1 to 8).
Another approach to weakening the affinity between LDH and carbonate ions is to weaken the interaction between the LDH layer and the interlayer anion by modifying the hydroxyl group on the outer surface of the LDH or the inner surface of the interlayer with an organic group. It has been devised to increase the anion exchange capacity. For example, Non-Patent Document 9 reports that the LDH surface is modified (complexed) with a covalently bonded alkoxy group by applying a coprecipitation method in monoalcohol.

K. H. Three people from K.-H. Goh, “Journal of Hazardous Materials”, 2010, Vol. 179, p818-827. Zet. Pee. 5 members from Z.P.Xu, “Journal of the American Chemical Society” 2006, 128, p36-37. Jay. A. J. A. Gursky and five others, “Journal of the American Chemical Society” 2006, Vol. 128, p. 8376-8377. Jay. 3 outside Prince (J. Prince), “Chemistry of Materials” 2009, Vol. 21, p 5826-5835. Wy. Three people from Y. Zhang, “Journal of Crystal Growth” 2010, Vol. 312, p3367-3372. tea. T. Hibino “Applied Clay Science” 2011, Vol. 54, p83-89. queue. Four people from Q. Wang, “Chemical Communications” 2012, Vol. 48, p7450-7451. tea. Two outside T. Hongo, “Chemistry Letters” 2006, Vol. 35, pp. 1296-1297. E. Two outside of E. Gardner, “Advanced Materials” 2001, Vol. 13, p 1263-1266.

As described above, various studies have been made to enable anion exchange with the layered double hydroxide even in the presence of carbon dioxide gas.
However, the amount of anion exchange sites located in the vicinity of the end portion between layers is suppressed by suppressing crystal growth during synthesis of LDH particles reported in Non-Patent Documents 1 to 8 and making LDH fine particles (nanoparticles). In the case of the method of increasing the number of particles, the crystal growth of the particles strongly depends on various synthesis conditions such as the metal concentration in the solution, pH, reaction time, reaction temperature, stirring speed, reaction scale, apparatus configuration, etc. There is a problem that it becomes complicated and difficult. For example, Non-Patent Document 8 reports the preparation of low-crystalline LDH having a crystallite size of 10 nm or less by a high-speed coprecipitation method without a ripening step. Control of operation is very difficult and cannot be practically used. Also disclosed in Non-Patent Document 9, which reported a method for weakening the interaction between the LDH layer and the interlayer anion and improving the anion exchange capacity by modifying the hydroxyl group on the outer surface of the LDH and the inner surface of the interlayer with an organic group. In LDH whose surface was modified (complexed) with a covalently bonded alkoxy group, the introduced alkoxy group easily hydrolyzed in water and was unstable.
As described above, all the methods of the conventional report examples have problems in terms of practicality and stability of the layered double hydroxide.
Layered double hydroxide is an extremely useful substance that can be expected to be used as an anion-conductive electrolyte membrane material for secondary batteries and fuel cells and various catalyst materials in addition to an anion exchanger for removing harmful metals. . Solving the problem of strong affinity of layered double hydroxides with carbonate ions is also important for further application development of layered double hydroxides, which are highly stable and carbon dioxide like in the atmosphere. There is a demand for the development of a layered double hydroxide capable of exhibiting good anion exchange ability even in the presence of gas.

The present invention has been made in view of the above situation, and has a high stability and a layered double hydroxide that exhibits a good anion exchange ability even in the presence of carbon dioxide gas, and such a layered double hydroxide. It aims at providing the manufacturing method of a thing.

The inventor conducted various studies on the layered double hydroxide having high stability and exhibiting good anion exchange ability even in the presence of carbon dioxide gas. As a result, the layered double hydroxide has two specific functional groups. When the composite layered double hydroxide is combined with the structural parts derived from the polyfunctional compound having the above, it can exist stably in water, and also exhibits a good anion exchange ability even in the presence of carbon dioxide gas. The inventors have found that it becomes a double hydroxide, and have reached the present invention.

That is, the present invention provides the following general formula (1);
^{_{M 2+ 1-x L 3+ x}} (OH) 2 A n- x / n · yH 2 O (1)
(In the formula, M represents a metal atom to be a divalent ion, L represents a metal atom to be a trivalent ion, and A ⁿ⁻ represents an n-valent anion. X represents 0 <x <1. Y represents a number of 0 or more, n represents a number of 1 to 3), a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol. A structural layer derived from a polyfunctional compound having two or more functional groups selected from the group consisting of a group is bonded at the binding site derived from the functional group, It is an oxide.
The present invention is described in detail below.
A combination of two or more preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

The composite layered double hydroxide of the present invention is at least one selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group in the layered double hydroxide represented by the general formula (1). A structural part derived from a polyfunctional compound having two or more kinds of functional groups is bonded. The reason why the composite layered double hydroxide of the present invention can exhibit good anion exchange ability even in the presence of carbon dioxide is presumed as follows.
That is, since the polyfunctional compound has a plurality of functional groups capable of forming a bond with the layered double hydroxide, when this polyfunctional compound is combined with the layered double hydroxide, it is derived from the functional group of the polyfunctional compound. It is considered that a bond is formed at a plurality of binding sites. As a result, a strong interaction is developed between the layered double hydroxide and the structural part derived from the polyfunctional compound, and the structural part derived from the polyfunctional compound is stably present in a state of being bonded to the layered double hydroxide. The presence of such a polyfunctional compound-derived structural moiety reduces the affinity between the layered double hydroxide and carbonate ion, and exhibits good anion exchange ability even in the presence of carbon dioxide gas. It is considered possible.

M in the general formula (1) is not particularly limited as long as it is a metal atom that becomes a divalent ion, and L in the general formula (1) is not particularly limited if it is a metal atom that becomes a trivalent ion. , M is at least one metal atom selected from the group consisting of Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, Zn, and L is Sc, Y, La, Ce, Pr, It is preferably at least one metal atom selected from the group consisting of Nd, Cr, Fe, Al, Ga, and In.
More preferably, M in the general formula (1) is at least one metal atom selected from the group consisting of Mg, Ca, Mn, Co, Ni, Cu, and Zn, and more preferably Mg, Ca, At least one metal atom selected from the group consisting of Ni, Cu and Zn.
More preferably, L in the general formula (1) is at least one metal atom selected from the group consisting of La, Ce, Cr, Fe, and Al, and more preferably a group consisting of Fe and Al. And at least one metal atom selected from the group.
Most preferably, M is Mg and L is Al from the viewpoint of cost, availability, and the like.

The polyfunctional compound is a compound having two or more functional groups selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group. Either a group or a silanol group is preferred.
The polyfunctional compound may have a plurality of the same kind of functional groups or may have a plurality of different types of functional groups, but preferably has a plurality of the same kind of functional groups. .

The polyfunctional compound is preferably a compound having three or more functional groups selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group.
When the polyfunctional compound has three or more functional groups, the structural part derived from the polyfunctional compound can exist more stably in a state where it is combined with the layered double hydroxide, and is good even in the presence of carbon dioxide gas. It is thought that an anion exchange ability can be exhibited.

The polyfunctional compound is not particularly limited as long as it has two or more functional groups selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group, The following general formula (2);
(XR ¹ ) _m C (R ² ) _4-m (2)
(In the formula, X represents a hydroxyl group, an amino group, a thiol group, a carboxyl group, or a silanol group. R ¹ represents a divalent hydrocarbon group having 1 to 4 carbon atoms. R ² represents a hydrogen atom. , A hydroxyl group, an amino group, a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a carboxyl group, wherein m represents an integer of 2 or more.
In this way, when the polyfunctional compound is a compound in which the same structural site (XR ¹ ) having a functional group is bonded to a carbon atom, the polyfunctional compound is layered double water at a plurality of bonded sites derived from the functional group. It is considered that a bond can be more stably formed with the oxide.
The preferable thing of X of the said General formula (2) is the same as the preferable thing of the functional group of the polyfunctional compound mentioned above.

In the general formula (2), R ¹ is preferably a divalent hydrocarbon group having 1 to 4 carbon atoms. More preferably, it is a C1-C2 bivalent hydrocarbon group. Most preferred is a divalent hydrocarbon group having 1 carbon atom, that is, a methylene group.
In the general formula (2), R ² is preferably a hydrogen atom, a hydroxyl group, an amino group, a monovalent hydrocarbon group having 1 to 4 carbon atoms, or a carboxyl group. More preferably, they are a hydroxyl group, an amino group, and a carboxyl group.
In the general formula (2), m is preferably any one of 2 to 3. Most preferably 3.

As the polyfunctional compound, a polyhydric alcohol is particularly preferable, and among them, a trivalent alcohol having three hydroxyl groups is more preferable. Most preferred is trishydroxymethylaminomethane (THAM).
Among the layered double hydroxides represented by the general formula (1), when manufacturing an MgAl type layered double hydroxide in which M is Mg and L is Al, the pH of the solution at the time of manufacture is About 9-10 is preferable.
When the composite layered double hydroxide of the present invention is produced by the method for producing the composite layered double hydroxide of the present invention, which will be described later, THAM is used, and when the concentration of THAM is adjusted, THAM has a pH buffer. As a result, the pH of the solution is 9 to 10, which is an optimum pH range in the case of producing an MgAl-type layered double hydroxide.

The composite layered double hydroxide of the present invention preferably has a particulate shape with an average particle size (average particle size) of 50 nm or less. As described above, the layered double hydroxide has a layered structure and a structure in which anions are coordinated between the layers. Among the anions present between the layers, the anion located near the edge of the layer (near the surface of the layered double hydroxide particle) is more mutually associated with the layer portion having a positive charge than the anion located inside the layer. It is considered that the action is weak and easy to exchange with other anions. When the composite layered double hydroxide is made finer, such as particles having an average particle size of 50 nm or less, it is closer to the end portion between the layers of the layered double hydroxide (near the surface of the layered double hydroxide particles). It is considered that the amount of anion exchange sites located increases and the anion exchange ability of the composite layered double hydroxide of the present invention increases. The average particle size of the composite layered double hydroxide is more preferably 30 nm or less, and still more preferably 20 nm or less. Moreover, it is preferable that an average particle diameter is 1 nm or more.
The average particle size of the composite layered double hydroxide particles can be measured with an electron microscope such as SEM or TEM, a laser diffraction particle size distribution measuring device, a dynamic light scattering particle size distribution measuring device, or the like. In the present invention, a measurement method by observation with an electron microscope such as SEM or TEM is used.

The present invention is also a method for producing a composite layered double hydroxide, which comprises a simple substance and / or compound of a metal atom to be a divalent ion and / or a simple substance of a metal atom to be a trivalent ion and / or Or a compound and a step of mixing a functional group-containing compound having at least one functional group selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group in a solution (hereinafter, also referred to as a mixing step) And a step of heating the solution obtained by mixing (hereinafter, also referred to as a heating step), and a method for producing a composite layered double hydroxide.

The method for producing a composite layered double hydroxide of the present invention can produce a desired composite layered double hydroxide in the form of fine particles (nanoparticles) with good reproducibility only by controlling the concentration of the functional group-containing compound in the raw material solution. Can be generated. This is considered to be because the binding site derived from the functional group of the functional group-containing compound binds to the surface of the layered double hydroxide as a ligand and promotes stabilization (aggregation suppressing effect) of the layered double hydroxide particles. . Thus, the method for producing a composite layered double hydroxide of the present invention can produce a composite layered double hydroxide in the form of fine particles (nanoparticles) with a simple operation and good reproducibility. This is a useful production method that is expected to be used in many ways.
The method for producing the composite layered double hydroxide of the present invention can also be suitably used as a method for producing the composite layered double hydroxide of the present invention described above. That is, the functional group-containing compound is a polyfunctional compound having two or more functional groups selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group. It is one of the suitable embodiment of the manufacturing method of a composite layered double hydroxide.

Examples of the metal atom to be a divalent ion and the metal atom to be a trivalent ion used in the method for producing a composite layered double hydroxide of the present invention include the same metal atoms as M and L in the above general formula (1). The preferred ones are also the same.
Examples of the metal atom that becomes a divalent ion or a metal atom that becomes a trivalent ion include chloride, oxide, sulfide, hydroxide, sulfate, nitrate, carbonate, phosphate, acetate, oxalic acid Salts, citrates, alkoxides, acetylacetonates and the like can be used. Among these, any of chloride, sulfate, nitrate, and acetate is preferable.
What is preferable as the functional group which the functional group-containing compound used in the method for producing the composite layered double hydroxide of the present invention has is the same as the preferable functional group which the polyfunctional compound described above has.

Selected from the group consisting of the simple substance and / or compound of a metal atom that becomes a divalent ion, the simple substance and / or compound of a metal atom that becomes a trivalent ion, and a hydroxyl group, amino group, thiol group, carboxyl group, and silanol group The solvent used for preparing the solution of the functional group-containing compound having at least one functional group is not particularly limited as long as it dissolves, and methanol, ethanol, propanol, butanol, water, acetone , Ethyl acetate, benzene, toluene, xylene, methyl ethyl ketone, cyclohexane, normal hexane or the like can be used. Among these, methanol, ethanol, and water are preferable, and water is more preferable.

The mixing step in the method for producing a composite layered double hydroxide of the present invention includes a simple substance and / or compound of a metal atom that becomes a divalent ion, a simple substance and / or compound of a metal atom that becomes a trivalent ion, and a hydroxyl group, As long as a functional group-containing compound having at least one functional group selected from the group consisting of an amino group, a thiol group, a carboxyl group, and a silanol group is to be mixed in the solution, these three types are added at once. However, it is also possible to mix any two of them in advance and then mix the remaining one. Usually, however, a simple substance and / or compound of a metal atom that becomes a divalent ion, and a trivalent A governmental solution having at least one functional group selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group, and a solution containing a simple substance and / or compound of metal atoms to be ions After preparing a solution containing a group containing compound, a method of mixing these solutions are used.

A simple substance and / or compound of a metal atom to be a divalent ion, a solution containing a simple substance and / or a compound of a metal atom to be a trivalent ion (hereinafter also referred to as a metal-containing solution), a hydroxyl group, an amino group, After preparing a solution containing a functional group-containing compound having at least one functional group selected from the group consisting of a thiol group, a carboxyl group, and a silanol group (hereinafter also referred to as a functional group-containing compound-containing solution), these When the step of mixing the solution of is performed, the molar ratio of the metal atom to be a divalent ion and the metal atom to be a trivalent ion in the metal-containing solution ([metal atom to be a divalent ion] / [trivalent ion] The metal atom]) is preferably 1/10 to 20/1. By mixing at such a molar ratio, the layered structure of the composite layered double hydroxide can be stably formed. More preferably, it is 1/2 to 5/1.
Further, the molar ratio of the total of metal atoms to be divalent ions and metal atoms to be trivalent ions in the metal-containing solution and the functional group-containing compound in the functional group-containing compound-containing solution ([metal to be divalent ions] The sum of atoms and metal atoms to be trivalent ions] / [functional group-containing compound]) is preferably 1/500 to 200/1. By mixing at such a molar ratio, the bond between the layered double hydroxide and the functional group-containing compound can be stably formed. More preferably, it is 1/200 to 50/1.

After preparing the said metal containing solution and a functional group containing compound containing solution, when performing the process of mixing these solutions, it is preferable to add a functional group containing compound containing solution to a metal containing solution. In this case, the addition method may be batch addition or sequential addition.

The heating step in the method for producing a composite layered double hydroxide of the present invention is preferably performed at a temperature of 30 to 300 ° C. By heating at such a temperature, aging of the composite layered double hydroxide proceeds, and the composite layered double hydroxide can be obtained in a high yield. More preferably, the temperature of a heating process is 40-200 degreeC, More preferably, it is 50-120 degreeC.
In consideration of both the sufficient aging of the composite layered double hydroxide and the production efficiency, the time for the heating step is preferably 0.5 to 50 hours. More preferably, it is 1-25 hours, More preferably, it is 1.5-15 hours.

The method for producing the composite layered double hydroxide of the present invention may include a step of purifying the obtained composite layered double hydroxide after the mixing step and the heating step, if necessary. The purification method is not particularly limited, and filtration, centrifugation, decantation and the like can be used.

The composite layered double hydroxide of the present invention has the above-described structure, and has a significantly low affinity with carbonate ions (CO ₃ ²⁻ ). Conditions under the presence of CO ₂ and conditions in which carbonate ions are incorporated as interlayer anions. Even in this case, nitrate ions (NO ₃ ⁻ ), hydrogen arsenate ions (HAsO ₄ ²⁻ ), selenate ions (SeO ₄ ²⁻ ), tetrahydroxyborate ions (B (OH) ₄ ⁻ ) And the like can be efficiently removed by anion exchange reaction. The composite layered double hydroxide of the present invention is expected to be used as a catalyst, a catalyst carrier, a drug carrier, an anion conductor, a host material of a nanocomposite, etc. by utilizing such a specific anion exchange ability. it can.
In addition, since the method for producing a composite layered double hydroxide of the present invention can produce desired fine particles (nanoparticles) with a good reproducibility by a simple operation, a useful composite expected to be used industrially. This is a method for producing a layered double hydroxide.

It is the figure which showed the structure of layered double hydroxide (LDH). The LDH is a structure having (1) a layer structure (Basal Layer) and (2) an interlayer part (Interlayer). In FIG. 1, (A) is OH ⁻ , (B) is a divalent metal ion, (C) is a trivalent metal ion, (D) is an anion (A ⁿ⁻ ), (E) is water ( H ₂ O) respectively. Composite layered double hydroxide 1 (LDHNP (10 nm)) synthesized in Examples 1 and 2, Composite layered double hydroxide 2 (LDHNP (25 nm)), and layered double hydroxide synthesized in Comparative Example 1 It is the figure which showed the SEM measurement result of a thing (LDH). (A) is a result of measuring LDHNP (10 nm), (b) is a result of measuring LDHNP (25 nm), and (c) is a result of measuring LDH. Composite layered double hydroxide 1 (LDHNP (10 nm)) synthesized in Examples 1 and 2, Composite layered double hydroxide 2 (LDHNP (25 nm)), and layered double hydroxide synthesized in Comparative Example 1 It is the figure which showed the XRD measurement result of the thing (LDH). (A) is a result of measuring LDHNP (10 nm), (b) is a result of measuring LDHNP (25 nm), and (c) is a result of measuring LDH. Composite layered double hydroxide 1 (LDHNP (10 nm)) synthesized in Examples 1 and 2, Composite layered double hydroxide 2 (LDHNP (25 nm)), and layered double hydroxide synthesized in Comparative Example 1 It is the figure which showed the FTIR measurement result of the thing (LDH). (A) is a result of measuring LDHNP (10 nm), (b) is a result of measuring LDHNP (25 nm), and (c) is a result of measuring LDH. FIG. 3 is a diagram showing a ¹³ C-NMR measurement result of a composite layered double hydroxide 1 (LDHNP (10 nm)) synthesized in Example 1. FIG. 4 is a diagram showing the SEM measurement result of the composite layered double hydroxide 3 synthesized in Example 3. FIG. 4 is a diagram showing an XRD measurement result of a composite layered double hydroxide 3 synthesized in Example 3. In the upper right frame of the figure, the particle size distribution of the composite layered double hydroxide 3 particles is shown. 6 is a diagram showing an SEM measurement result of a composite layered double hydroxide 4 synthesized in Example 4. FIG. FIG. 6 is a view showing an XRD measurement result of the composite layered double hydroxide 4 synthesized in Example 4. In the upper right frame of the figure, the particle size distribution of the composite layered double hydroxide 4 particles is shown. NO ₃ composite layered double hydroxide (LDHNP) and layered double hydroxide (LDH) ^- A diagram showing the results of anion exchange capacity evaluation. (A) LDHNP (10 nm), (b) LDHNP (25 nm), (c) LDH, (d) LDHNP (10 nm) -as. A diagram showing the results of unit intervals of the layer structure after anion exchange (Basal Spacing) was measured ^- NO ₃ composite layered double hydroxide (LDHNP) and layered double hydroxides (LDH). (A) LDHNP (10 nm), (b) LDHNP (25 nm), (c) LDH, (d) LDHNP (10 nm) -as.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by weight” and “%” means “mass%”.

Various measurements in the examples were performed by the following equipment and methods.
<Electron microscope (SEM) measurement>
Using a Hitachi S-4700 microscope, a colloidal solution or a powder sample was dispersed in ethanol and dropped onto a carbon-coated Cu grid.
<FTIR measurement>
It was measured by KBr plate method using Jasco FT / IR-4100.
< ^13C -NMR measurement>
The measurement was carried out using a Chemicals CMX-300 Infinity at 76.5 MHz, a contact time of 5.0 ms, and a repetition time of 5 seconds.
<XRD measurement>
Measurement was performed using a Rigaku Smartlab diffractometer using CuKα rays (45 kV, 200 mA).
<Elemental analysis>
Measurement was performed by inductively coupled plasma analysis using Shimadzu ICPS-8100.

Example 1 (Synthesis of composite layered double hydroxide 1 (LDHNP (10 nm)))
In a polypropylene container, put MgCl ₂ · 6H ₂ O, AlCl ₃ · 6H ₂ O and water so that the concentration of MgCl ₂ is 13.1 mM and AlCl ₃ is 6.9 mM, and the total liquid volume is 100 ml. Mixed (referred to as aqueous solution 1). Separately from the aqueous solution 1, trishydroxymethylaminomethane (THAM) and water were put into a beaker and mixed so that the concentration of trishydroxymethylaminomethane (THAM) was 2.0 M and the total amount of liquid was 100 ml. (Referred to as aqueous solution 2). The aqueous solution 2 was added to the aqueous solution 1 at a time, mixed, and then allowed to stand at 80 ° C. for 12 hours in an airtight polypropylene container for aging. After aging, a part of the solution in which the produced composite layered double hydroxide was dispersed was subjected to SEM measurement. The remaining solution was filtered through a membrane filter having a pore size of 0.2 μm. The obtained composite layered double hydroxide was dispersed again in an aqueous Na ₂ CO ₃ solution (0.5 M) and stirred for 1 hour to exchange all the anions between the layers of the layered double hydroxide with CO ₃ ²⁻ . Thereafter, the redispersion was filtered. The obtained composite layered double hydroxide was washed twice with deionized water and filtered twice, and the resulting gel composite layered double hydroxide was dried at 80 ° C. and finely crushed in a mortar. (Particulate) composite layered double hydroxide 1 (LDHNP (10 nm)) was obtained. The SEM measurement results are shown in FIG. 2, and the XRD measurement results of the obtained composite layered double hydroxide 1 are shown in FIG.
Moreover, the FTIR measurement result is shown in FIG. The 1087 cm ^-1 and 1135 cm ^-1 bands are due to the stretching vibrations of M-O-C and C-C-O, respectively, suggesting that THAM is coordinated inside and outside the surface of LDHNP. To do.
Moreover, the ¹³ C-NMR measurement result of the composite layered double hydroxide 1 is shown in FIG. In FIG. 5, broken lines (i) to (iv) indicate signal analysis results. The signals of 58.8 ppm (iii) and 70.6 ppm (ii) are attributed to the free methylene carbon (—CH ₂ O—) and the coordinated THAM methylene carbon, respectively. The signal of 50.5 ppm (iv) is attributed to the quaternary carbon (—CNH ₂ ) of THAM coordinated to the layered double hydroxide (LDH) as an alkoxide species. The signal of 168.3 ppm is attributed to the carbon of CO ₃ ²⁻ .

Example 2 (Synthesis of composite layered double hydroxide 2 (LDHNP (25 nm)))
A composite layered double hydroxide 2 (LDHNP (25 nm)) was synthesized in the same manner as in Example 1 except that a 0.5M THAM solution was used and the MgCl ₂ concentration in the aqueous solution was 15 mM and the AlCl ₃ concentration was 5 mM. The SEM measurement result of the composite layered double hydroxide 2 is shown in Fig. 2, the XRD measurement result is shown in Fig. 3, and the FTIR measurement result is shown in Fig. 4.

Comparative Example 1 (Synthesis of layered double hydroxide (LDH))
In a beaker, MgCl ₂ · 6H ₂ O, AlCl ₃ · 6H ₂ O and water were added, and mixed so that the concentration of MgCl ₂ was 333 mM and AlCl ₃ was 167 mM, and the total amount of the solution was 30 ml (aqueous solution 3 And). The aqueous solution 3 was added dropwise at room temperature to an aqueous Na ₂ CO ₃ solution having a concentration of 0.1 M and a liquid volume of 50 ml. In the meantime, a 2.0 M NaOH aqueous solution was appropriately added so that the pH of the solution was maintained at 10. After completion of dropping, the solution was allowed to stand at 80 ° C. for 12 hours for aging. The deposited precipitate was filtered with a filter paper, washed with water, and dried at 80 ° C. to obtain a layered double hydroxide.
The SEM measurement result of the obtained layered double hydroxide is shown in FIG. 2, and the XRD measurement result is shown in FIG. Moreover, the FTIR measurement result is shown in FIG.
Table 1 shows the crystallite size and average particle size of LDHNP (10 nm) and LDHNP (25 nm) synthesized in Examples 1 and 2 and LDH synthesized in Comparative Example 1, and Table 2 shows the component composition (molar ratio).
In Table 1, “D _hkl ” represents the crystallite size in the [hkl] direction (crystallite size calculated from the [hkl] diffraction peak obtained by XRD measurement). The size of secondary particles formed by collecting several crystallites (primary particles) is considered to correspond to the average particle size (general average particle size) measured by SEM.

Example 3 (Synthesis of composite layered double hydroxide 3)
A composite layered double hydroxide 3 was synthesized in the same manner as in Example 1 except that a 1M aqueous solution of L-lysine was used instead of the 2.0M aqueous solution of THAM. The SEM measurement result of the composite layered double hydroxide 3 is shown in FIG. 6, and the XRD measurement result is shown in FIG. D ₀₀₃ and D ₁₁₀ were 9.7 nm and 20.1 nm, respectively, and the average particle size by SEM measurement was 47.9 nm.

Example 4 (Synthesis of composite layered double hydroxide 4)
A composite layered double hydroxide 4 was synthesized in the same manner as in Example 1 except that a 1M aqueous solution of 2-amino-1,3-propanediol was used instead of the 2.0M aqueous solution of THAM. The SEM measurement result of the composite layered double hydroxide 4 is shown in FIG. 8, and the XRD measurement result is shown in FIG. D ₀₀₃ and D ₁₁₀ were 9.7 nm and 20.7 nm, respectively, and the average particle size by SEM measurement was 30.7 nm.

Example 5 (Synthesis of composite layered double hydroxide 5 (LDHNP (10 nm) -as))
In Example 1, the produced LDHNP was dispersed again in an aqueous Na ₂ CO ₃ solution (0.5 M), and the same procedure as in Example 1 was performed, except that the operation of exchanging all the anions between the layers with CO ₃ ²⁻ was not performed. Thus, composite layered double hydroxide 5 (LDHNP (10 nm) -as) was synthesized.

Example 6 (Evaluation of anion exchange capacity)
The composite layered double hydroxides 1, 2, 5 synthesized in Examples 1, 2, 5 and the layered double hydroxide synthesized in Comparative Example 1 were each added to a 1.0 M aqueous solution of NaNO ₃ at 2 mg / mL. The resulting solution was added to a concentration of 1, and stirred for 2 hours in a normal air atmosphere. Thereafter, the composite layered double hydroxides 1, 2, 5, and the layered double hydroxide were collected by filtration, washed twice with water and once with acetone, and dried at room temperature. The amount of NO ₃ ⁻ ions in the composite layered double hydroxide 1, 2, 5 and the layered double hydroxide after drying was quantified by elemental analysis. Further, the unit spacing (basal spacing) of the layer structure of the composite layered double hydroxides 1, 2, 5 and the layered double hydroxide was measured by XRD. The same operation was performed by changing the concentration of the NaNO ₃ aqueous solution to 2.5M, 5.0M, and 10.0M.
NO ₃ ^- in Figure 10 the measurement results of the amount of ions, NO ₃ ^- Figure 11 shows the measurement results of the unit interval of a layer structure after ion exchange (Basal Spacing).
In addition, the unit interval (Basal Spacing) of the layer structure corresponds to the width of the Basal Layer 1 layer + Interlayer 1 layer. Even if anion exchange occurs, the width of Basal Layer does not change. Therefore, the expansion of Basal Spacing is considered to mean that the Interlayer (interlayer) is expanded.
In FIG. 10, NO ₃ ⁻ / Al ³⁺ value was used as the theoretical anion exchange rate, and THAM was not lost in the process of anion exchange, and the minimum value was plotted. NO ₃ ^- width / ^{Al 3+} is possible values are expressed in the plot above the error bars.
In FIG. 11, Basal Spacing when the anion between layers is completely substituted with NO ₃ ^— with LDH (Mg / Al = 2) is 0.89 nm.

Example 7 (Evaluation of removal performance of harmful oxyanions)
A solution prepared by dissolving Na ₂ HAsO ₄ .7H ₂ O and Na ₂ SeO ₄ in water and a standard solution of boron for atomic absorption analysis were used as harmful oxyanion solutions.
Both the HAsO ₄ ^2- and SeO ₄ ^2- solutions had a pH of 8. The boron solution was adjusted to pH 11 using 1M NaOH solution. In this condition, boron is mainly _{(BOH) 4} ^- are present as. The composite layered double hydroxide 5 (LDHNP (10 nm) -as) synthesized in Example 5 was added to the harmful oxyanion solution and stirred at room temperature for 2 hours, and anion exchange with the harmful oxyanion (of harmful oxyanion was performed). Adsorption removal). Thereafter, the composite layered double hydroxide was recovered by filtration through a membrane filter having a pore size of 0.2 μm, and the concentration of each anion was measured by ICP. The same operation was performed by adding the layered double hydroxide (LDH) of Comparative Example 1 to the harmful oxyanion solution, and the concentration of each anion was measured by ICP. The measurement is performed by adjusting the addition amount so that the concentrations of LDHNP (10 nm) -as and LDH in the harmful oxyanion solution are 0.01% by mass, 0.10% by mass and 1.0% by mass, respectively. It was. The results are shown in Table 3.

From the results of Table 1 and Examples 3 and 4, in the composite layered double hydroxide (LDHNP) of Examples 1 to 4, compared to the layered double hydroxide (LDH) of Comparative Example 1, the crystallite size and It was confirmed that the average particle size was small. From the XRD measurement results, it was confirmed that the composite layered double hydroxide (LDHNP) of Examples 1 to 4 and the layered double hydroxide (LDH) of Comparative Example 1 were both MgAl type LDH. From this, it was shown that the crystallite size and the average particle size were reduced by the action of THAM. In addition, the lattice spacing (d ₀₀₃ value) obtained from the [003] diffraction peak position in the XRD measurement of the composite layered double hydroxide 1, particularly the composite layered double hydroxide 1 (LDHNP (10 nm)) is layered composite. It is larger than the value of hydroxide (LDH), suggesting that THAM exists not only outside the layered double hydroxide but also between the layers.
Looking at the results of elemental analysis in Table 2, the Mg / Al ratio of LDH is about 2, which is the upper limit value of Al ³⁺ entering the LDH layer, and LDH has the highest anion exchange capacity. ing. The theoretical value of the anion exchange capacity of LDH corresponds to the amount of Al ^{3+ in} the brucite layer, and is a composite layered double hydroxide 2 (LDHNP (25 nm)) and a layered double hydroxide (LDH). The amount of CO ₃ ²⁻ is almost the same as the amount estimated from the amount of Al ³⁺ . On the other hand, in the case of the composite layered double hydroxide 1 (LDHNP (10 nm)), the amount of CO ₃ ²⁻ is larger than the amount estimated from the amount of Al ³⁺ . This is thought to be due to the formation of additional anion exchange sites derived from THAM amino groups and / or broken bonds at the ends of the composite layered double hydroxide.

Composite layered double hydroxide 3 or composite layered double hydroxide produced using 1M aqueous solution of L-lysine or 1M aqueous solution of 2-amino-1,3-propanediol instead of 2.0M aqueous solution of THAM In FIG. 4, the crystallite size and the average particle size are smaller than those of the layered double hydroxide (LDH). When the composite layered double hydroxide 3 or 4 was produced, the pH of the composite layered double hydroxide was kept at 9.6 to 10.1 (a value close to that when THAM was used). The size was larger than when THAM was used, and sharper peaks were observed in the XRD pattern than in the composite layered double hydroxides 1 and 2 using THAM. From this result, the crystallite size and average particle size of the composite layered double hydroxide obtained using THAM were reduced because THAM coordinated to LDH rather than acting as a pH buffer for THAM. Therefore, it is considered that the influence by suppressing the aggregation of LDH is great.

From exchange capacity evaluation results of the anion, the layered double hydroxide _{^{(LDH), NO 3 - -}} NO 3 shown in FIG. 10 while not proceed little exchange with anion, composite layered double hydroxides ( In LDHNP), it was confirmed that anion exchange proceeds. Compared with the case of NaNO ₃ 10M solution, the anion exchange capacity was 48% for the composite layered double hydroxide 1 (LDHNP (10 nm)) and 36% for the composite layered double hydroxide 2 (LDHNP (25 nm)). , Composite layered double hydroxide 5 (LDHNP (10 nm) -as) is 73%, and composite layered double hydroxide 5 (LDHNP (10 nm) -as) containing Cl ⁻ and CO ₃ ²⁻ as anions is used. ) Resulted in the highest anion exchange capacity.
In the graph of the unit spacing (Basal Spacing) of the layer structure in FIG. 11, in the composite layered double hydroxide (LDHNP), Basal Spacing spreads more than the layered double hydroxide (LDH), and THAM is arranged between the layers. It is thought that it is ranked. Regarding LDHNP (10 nm) and LDHNP (10 nm) -as, the interlayer distance decreases in the case of 1M NaNO ₃ solution because the THAM present between the layers is desorbed from the LDH surface during the ion exchange operation, There is a possibility that it was missing.

From the results of evaluating the removal performance of harmful oxyanions in Table 3, it was confirmed that the composite layered double hydroxide (LDHNP) has an excellent removal performance of harmful oxyanions compared to the layered double hydroxide (LDH). It was. The values after adsorption of As and Se using LDHNP (10 nm) -as were both below the detection limit. The detection limit was determined by 3.3 s of the blank sample response. The value after adsorption of B using LDHNP (10 nm) -as is the value after the adsorption is carried out twice continuously. The value after the first adsorption was 22.5 ppm (77.8% removal).

(1): Layer structure (Basal Layer)
(2): Interlayer part
(A): OH ⁻
(B): Divalent metal ion (C): Trivalent metal ion (D): Anion (A ⁿ⁻ )
(E): Water (H ₂ O)

Claims (5)

The following general formula (1);
^{_{M 2+ 1-x L 3+ x}} (OH) 2 A n- x / n · yH 2 O (1)
(In the formula, M represents a metal atom to be a divalent ion, L represents a metal atom to be a trivalent ion, and A ⁿ⁻ represents an n-valent anion. X represents 0 <x <1. Y represents a number of 0 or more, and n represents a number of 1 to 3.) In the layered double hydroxide represented by the following general formula (2);
(XR ¹ ) _m C (R ² ) _4-m (2)
(In the formula, X represents a hydroxyl group, an amino group, a thiol group, a carboxyl group, or a silanol group. R ¹ represents a divalent hydrocarbon group having 1 to 4 carbon atoms. R ² represents a hydrogen atom. , A hydroxyl group, an amino group, a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a carboxyl group, and m represents an integer of 2 or more). A composite layered double hydroxide characterized by being bonded at a binding site derived from the functional group. M in the general formula (1) is at least one metal atom selected from the group consisting of Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, and Zn, and L is Sc, Y 2. The composite layered double hydroxide according to claim 1, which is at least one metal atom selected from the group consisting of La, Ce, Pr, Nd, Cr, Fe, Al, Ga, and In. object. The polyfunctional compound is a compound having at least three functional groups selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, and a silanol group. The composite layered double hydroxide described in 1. The composite layered double hydroxide according to any one of claims 1 to 3, wherein the composite layered double hydroxide has a particle shape having an average particle diameter of 50 nm or less. A method for producing a composite layered double hydroxide, the production method comprising:
Simple substance and / or compound of a metal atom to be a divalent ion, simple substance and / or compound of a metal atom to be a trivalent ion, and the following general formula (2);
(XR ¹ ) _m C (R ² ) _4-m (2)
(In the formula, X represents a hydroxyl group, an amino group, a thiol group, a carboxyl group, or a silanol group. R ¹ represents a divalent hydrocarbon group having 1 to 4 carbon atoms. R ² represents a hydrogen atom. , A hydroxyl group, an amino group, a monovalent hydrocarbon group having 1 to 4 carbon atoms and a carboxyl group, m represents an integer of 2 or more) and a functional group-containing compound having a structure represented by And a process of
And a step of heating the solution obtained by mixing. A method for producing a composite layered double hydroxide, comprising: