JP2016084264A - Method for forming layered double hydroxide dense film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a highly densified LDH dense film on a surface of a substrate without unevenness uniformly.SOLUTION: There is provided a method for forming layered double hydroxide dense film on a surface of a substrate, where the layered double hydroxide dense film consists of layered double hydroxide represented by the general formula:MM(OH)AmHO, where Mis bivalent cation, Mis trivalent cation, Ais n valent anion, n is an integer of 1 or more and x is 0.1 to 0.4, including (a) a process for preparing the substrate exhibiting a negative zeta potential substantially whole region of pH 5 to 8 and (b) a process for conducting a hydrothermal treatment on the substrate in a raw material solution containing constituent elements of the layered double hydroxide to form the layered double hydroxide dense film on the surface of the substrate.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for forming a layered double hydroxide dense film, and more specifically to a method for forming a layered double hydroxide dense film on the surface of a substrate.

  Layered Double Hydroxide (hereinafter also referred to as LDH) typified by hydrotalcite is a group of substances having anions that can be exchanged between hydroxide layers. It is used as a catalyst, an adsorbent, and a dispersant in a polymer for improving heat resistance. In particular, in recent years, it has been attracting attention as a material that conducts hydroxide ions, and addition to an electrolyte of an alkaline fuel cell or a catalyst layer of a zinc-air cell has also been studied.

  When considering catalysts and the like which are conventional application fields, synthesis and use in powdered LDH was sufficient because a high specific surface area was required. On the other hand, when considering application to an electrolyte utilizing hydroxide ion conductivity such as an alkaline fuel cell, a highly dense LDH film is desirable in order to prevent mixing of fuel gas and obtain sufficient electromotive force. It is.

  Patent Documents 1 and 2 and Non-Patent Document 1 disclose an oriented LDH film. The oriented LDH film suspends the surface of a polymer base material horizontally in a solution containing urea and a metal salt to nucleate LDH. It is produced by forming and orientation growing. In each of the X-ray diffraction results of the oriented LDH thin films obtained in these documents, a strong peak of (003) plane is observed.

Chinese registered patent gazette CNC 1333113 International Publication No. 2006/050648

ZhiLu, Chemical Engineering Science 62, pp. 6069-6075 (2007), “Microstructure-controlled synthesis of oriented layered double hydroxide thin films: Effect of varying the preparation conditions and a kinetic and mechanistic study of film formation”

  The present inventors have succeeded in producing a dense bulk body of LDH (hereinafter referred to as an LDH dense body). In addition, while conducting evaluation of hydroxide ion conductivity for LDH dense bodies, it has been found that high conductivity is exhibited by conducting ions in the layer direction of LDH particles. However, when considering application of LDH as a solid electrolyte separator to an alkaline secondary battery such as a zinc-air battery or a nickel-zinc battery, there is a problem that the LDH dense body has high resistance. Therefore, for practical use of LDH, it is desired to reduce the resistance by thinning. In this regard, the oriented LDH film disclosed in Patent Documents 1 and 2 and Non-Patent Document 1 cannot be said to be sufficient in terms of orientation and density. Therefore, a highly densified LDH film, preferably an oriented LDH film is desired. However, it is not always easy to uniformly form an LDH dense film on a substrate. In particular, when an attempt is made to form an LDH dense film on a substrate, variations in density are likely to occur, and a technique for reliably and uniformly forming an LDH dense film on the entire surface of the substrate is desired.

  The present inventors have recently prepared a substrate exhibiting a negative zeta potential in a substantially entire range of pH 5 to 8, and by forming an LDH dense film on the surface by hydrothermal treatment, the surface of the substrate is formed. The present inventors have found that a highly densified LDH dense film can be uniformly formed without unevenness.

  Accordingly, an object of the present invention is to provide a method for uniformly and uniformly forming a highly densified LDH dense film on the surface of a substrate.

According to one aspect of the present invention, there is provided a method for forming a layered double hydroxide dense film on a surface of a substrate, wherein the layered double hydroxide dense film has the general formula: M ²⁺ _1-x M ³⁺ _{x (OH)} in _{^{2 a n- x / n · mH}} 2 O ( ^{wherein, M 2+} is a divalent ^{cation, M 3+} is a trivalent ^{cation, a n-n-valent} anion, n represents An integer of 1 or more, x is 0.1 to 0.4)
(A) a step of preparing a substrate exhibiting a negative zeta potential in a substantially entire range of pH 5 to 8,
(B) in a raw material aqueous solution containing the constituent element of the layered double hydroxide, the substrate is hydrothermally treated to form the layered double hydroxide dense film on the surface of the substrate;
A method is provided comprising:

It is a schematic cross section which shows one aspect | mode of the LDH containing composite material obtained by the method of this invention. It is a schematic cross section which shows another one aspect | mode of a LDH containing composite material. It is a schematic diagram which shows a layered double hydroxide (LDH) plate-like particle. It is a SEM image which shows the surface microstructure of the film | membrane sample observed in Examples A1-A5. It is a figure which shows the zeta potential in various pH of the polystyrene base material used for Example A1 and A2. It is a figure which shows the zeta potential in various pH of the 3YSZ base material (Example A3 and A4) and the titania base material (Example A5) used for Examples A3-A5. It is a transmission spectrum of the polystyrene board which carried out the sulfonation process by each concentrated sulfuric acid immersion time measured by the ATR method of FT-IR in Example B1. It is the XRD profile obtained with respect to the crystal phase of the sample 9 in Example B2. It is a SEM image which shows the surface microstructure of the samples 1-6 observed in Example B3. It is a SEM image which shows the surface microstructure of the samples 9-16 observed in Example B3. It is a SEM image which shows the surface microstructure of the comparative sample 18 observed in Example B3. It is a SEM image of the fracture | rupture cross-sectional microstructure of the sample 9 observed in Example B3. It is a SEM image of the grinding | polishing cross-section microstructure of the sample 9 observed in Example B3. It is a SEM image of the grinding | polishing cross-section microstructure of the sample 2 observed in Example B3. It is a disassembled perspective view of the density discrimination | determination measurement system used for a density determination test. It is a schematic cross section of a denseness discrimination measurement system used for a denseness judgment test.

Forming method The present invention LDH dense film, a method of forming a layered double hydroxide dense film (LDH dense film) on the surface of the substrate. The substrate may be a nonporous substrate or a porous substrate. In the case of a porous substrate, the “surface of the substrate” mainly refers to the outermost surface of the plate surface when the general shape of the porous substrate is viewed macroscopically as a plate. Needless to say, the surface of the hole existing in the vicinity of the outermost surface of the plate surface can be included incidentally. LDH dense membranes, the general ^{_{formula: M 2+ 1-x M 3+}} x (OH) in _{2 A n- x / n · mH} 2 O ( ^{wherein, M 2+} is a divalent ^{cation, M 3+} is a trivalent cation It is an ion, and A ⁿ⁻ is an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4), and is composed of a layered double hydroxide (LDH). In the above general formula, M ²⁺ may be any divalent cation, and preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ may be any trivalent cation, but preferred examples include Al ³⁺ or Cr ³⁺ , and more preferred is Al ³⁺ . A ^n- may be any anion, preferred examples OH ^- and _CO ^{3 2-} and the like. Therefore, in the general ^{formula, M 2+} comprises ^{Mg 2+, M 3+} comprises ^{Al 3+, A n-is} OH ^- and / or _CO preferably contains ^{3 2-.} n is an integer of 1 or more, preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is an arbitrary real number.

The formation of an LDH dense film by the method of the present invention comprises: (a) preparing a substrate exhibiting a negative zeta potential in substantially the entire pH range of 5 to 8, and (b) subjecting the substrate to hydrothermal treatment in an aqueous raw material solution, This is done by forming a dense film. As described above, a substrate exhibiting a negative zeta potential in a substantially entire range of pH 5 to 8 is prepared, and a highly dense LDH film is formed on the surface by hydrothermal treatment, whereby the surface of the substrate is highly dense. The formed LDH dense film can be uniformly formed without unevenness. As described above, when an attempt is made to form an LDH dense film on a substrate (particularly a ceramic substrate), variation in density is likely to occur, and a technique for reliably and uniformly forming an LDH dense film on the entire surface of the substrate is desired. . In this regard, according to the above-described method of the present invention, the substrate has a negative zeta potential in a substantially entire range of pH 5 to 8 (which is a main liquid region in which the raw material aqueous solution passes through the film formation process of LDH by hydrothermal treatment). It is considered that nucleation and growth of LDH are promoted by the following mechanism. That is, (i) a negative zeta potential of the substrate is brought about by an anionic group (which can constitute an intermediate layer of LDH) attached to the substrate, thereby incorporating the anionic group as an intermediate layer. LDH nuclei are formed from which LDH grows. (Ii) Positively charged metal ions (that is, metal ions of LDH constituent elements such as Mg ²⁺ and Al ³⁺ ) are electrostatically charged on the negatively charged substrate surface. The adsorbed metal ions form LDH nuclei from which LDH grows and / or (iii) negatively charged LDH nuclei adsorb on the negatively charged substrate surface Then, a mechanism that LDH grows from there is assumed. In any case, according to the above-described method of the present invention, the starting points of LDH crystal growth can be uniformly provided on the substrate, and LDH crystal growth can be promoted uniformly from these starting points. As a result, a highly densified LDH dense film can be uniformly formed on the surface of the substrate without unevenness.

(A) Preparation of Substrate In this step (a), a substrate exhibiting a negative zeta potential is prepared over a substantially entire range of pH 5 to 8, preferably pH 4 to 8, and more preferably pH 3 to 8. The base material may exhibit a negative zeta potential as an inherent property, or a group that does not originally have such a zeta potential but has been subjected to a surface treatment and subsequently given a negative zeta potential. It may be a material. The base material is preferably composed of at least one selected from the group consisting of ceramic materials, metal materials, and polymer materials. Preferred examples of ceramic materials include alumina, zirconia, titania, magnesia, spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, aluminum nitride, silicon nitride, and any combination thereof. More preferred are alumina, zirconia, titania, and any combination thereof, and particularly preferred are alumina, zirconia (eg, yttria stabilized zirconia (YSZ)), and combinations thereof. When these ceramics are used, it is easy to improve the denseness of the LDH dense film. Preferable examples of the metal material include aluminum and zinc. Preferred examples of the polymer material include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, and any combination thereof. Any of the various preferred materials described above has alkali resistance as resistance to the electrolyte of the battery. When using a base material, it is preferable to perform ultrasonic cleaning, cleaning with ion-exchanged water, or the like on the base material.

  When a negative zeta potential is subsequently applied to the substrate, the step (a) is positive in at least part of the pH range of (a1) pH 5-8 (preferably pH 4-8, more preferably pH 3-8). A step of preparing a substrate exhibiting a zeta potential of (a2) on the surface of the substrate, the surface having a negative zeta potential in substantially the entire region of pH 5 to 8 (preferably pH 4 to 8, more preferably pH 3 to 8). And a step of performing a surface treatment so as to exhibit. The surface treatment in the step (a2) is not particularly limited as long as it is a technique capable of applying the negative zeta potential, but (i) sulfonating the surface of the base material, ii) at least one selected from the group consisting of treating the surface of the substrate with a surfactant, treating the surface of the substrate with plasma, and (iii) treating the surface of the substrate with acid or alkali. Is preferably performed.

(I) Sulfonation of substrate surface Sulfonation of the substrate surface in the step (a2) may be performed by any method as long as a negative zeta potential can be applied to the substrate. For example, the sulfonation treatment may be carried out by converting a sulfonateable substrate or a sulfonateable surface-treated substrate into a sulfonateable acid such as sulfuric acid (for example, concentrated sulfuric acid), fuming sulfuric acid, chlorosulfonic acid, and anhydrous sulfuric acid. What is necessary is just to immerse and you may use another sulfonation technique. The immersion in the sulfonateable acid may be performed at room temperature or high temperature (for example, 50 to 150 ° C.), and the immersion time is not particularly limited, but is, for example, 1 to 14 days. Preferable examples of the substrate capable of being sulfonated include a polymer substrate. The polymer substrate capable of being sulfonated is preferably composed of at least one selected from the group consisting of polystyrene, polyethersulfone, polypropylene, epoxy resin, and polyphenylene sulfide. In particular, the aromatic polymer base material is preferable in that it is easily sulfonated, and such an aromatic polymer base material is selected from the group consisting of polystyrene, polyethersulfone, epoxy resin, and polyphenylene sulfide, for example. Most preferably, it consists of polystyrene. Alternatively, sulfonation can be carried out in the same manner as the above-described sulfonateable substrate, if surface treatment is performed so that sulfonation is possible even if the substrate is not sulfonateable or is not suitable for sulfonation. Such surface treatment is preferably performed by attaching a polymer to the substrate, and as such a polymer, it is preferable to use a polymer material similar to the above-described sulfonateable polymer substrate. Further, the polymer is preferably attached to the substrate by applying a solution in which the polymer is dissolved (hereinafter referred to as a polymer solution) to the surface of the substrate. The polymer solution can be easily prepared, for example, by dissolving a polymer solid (for example, a polystyrene substrate) in an organic solvent (for example, a xylene solution). When the substrate is porous, it is preferable to prevent the polymer solution from penetrating into the porous substrate because it is easy to achieve uniform coating. In this respect, the polymer solution is preferably attached or applied by spin coating because it can be applied uniformly.

(Ii) Surfactant treatment on substrate surface The surfactant treatment on the substrate surface in the step (a2) may be performed by any method as long as a negative zeta potential can be imparted to the substrate. The surfactant is not particularly limited as long as it can give a negative zeta potential to the surface of the substrate, but an anionic surfactant is preferable. Such a surfactant may contain a hydrophilic group (for example, —SO ₃ H or O—SO ₃ H) that gives an anion that can be a part of the LDH structure. It may contain a hydrophilic group (for example, —COOH or O—P (OH) ₃ ) that gives an anion that does not become a part. Preferable examples of the anionic surfactant include a sulfonic acid type anionic surfactant, a sulfate ester type anionic surfactant, a phosphate ester type anionic surfactant, a carboxylic acid type anionic surfactant, and the like. Any combination of these may be mentioned. Examples of the sulfonic acid type anionic surfactant include naphthalene sulfonic acid Na formalin condensate, polyoxyethylene sulfosuccinic acid alkyl 2Na, polystyrene sulfonic acid Na, dioctyl sulfosuccinic acid Na, polyoxyethylene lauryl ether sulfate triethanolamine. It is done. Examples of the sulfate ester type anionic surfactant include polyoxyethylene lauryl ether sulfate Na. Examples of carboxylic acid type anionic surfactants include polycarboxylic acid type anionic surfactants and polyoxyethylene lauryl ether acetate Na. The treatment of the substrate with the surfactant is not particularly limited as long as it is a technique capable of attaching the anionic hydrophilic group of the surfactant or the anion derived therefrom to the surface of the substrate. It is preferable to carry out by applying the solution containing the solution to the substrate or immersing the substrate in a solution containing the surfactant. This treatment is more preferably performed by immersing the substrate in a solution containing a surfactant. In this case, the immersion of the base material in the solution containing the surfactant may be performed at room temperature or higher temperature (for example, 40 to 80 ° C.) while stirring the solution, and the immersion time is not particularly limited. ~ 7 days.

(Iii) Acid or alkali treatment of the substrate surface The acid or alkali treatment of the substrate surface in the step (a2) may be performed by any method as long as a negative zeta potential can be imparted to the substrate. Preferred examples of such acids include sulfuric acid, hydrochloric acid, and nitric acid. Preferred examples of such an alkali include aqueous ammonia, sodium hydroxide, and sodium carbonate.

  By the way, the substrate may be a porous substrate. Since the substrate supporting the LDH film is porous, hydroxide ions in the electrolytic solution can be moved through the LDH film when the application of the LDH film as a solid electrolyte separator is considered. The porous base material is not particularly limited as long as it can form a desired LDH dense film on the surface thereof. In any case, it is preferable that the porous base material has a porous structure having water permeability in that the electrolyte solution can reach the LDH film when incorporated into a battery as a battery separator. More preferably, the porous substrate is made of a ceramic material. The porous substrate made of a ceramic material may be a commercially available product or may be prepared according to a known technique, and is not particularly limited. For example, ceramic powder (for example, zirconia powder (for example, YSZ powder), boehmite powder, titania powder, etc.), methylcellulose, and ion-exchanged water are kneaded at a desired blending ratio, and the obtained kneaded product is subjected to extrusion molding to obtain The obtained molded body is dried at 70 to 200 ° C. for 10 to 40 hours, and then fired at 900 to 1300 ° C. for 1 to 5 hours, whereby a porous substrate made of a ceramic material can be produced. The blending ratio of methylcellulose is preferably 1 to 20 parts by weight with respect to 100 parts by weight of the ceramic powder. Further, the blending ratio of the ion exchange water is preferably 10 to 100 parts by weight with respect to 100 parts by weight of the ceramic powder.

  The porous substrate preferably has an average pore diameter of 0.001 to 1.5 μm, more preferably 0.001 to 1.25 μm, still more preferably 0.001 to 1.0 μm, and particularly preferably 0.001. It is -0.75 micrometer, Most preferably, it is 0.001-0.5 micrometer. By setting it within these ranges, it is possible to form an LDH dense membrane that is so dense that it does not have water permeability (desirably water permeability and air permeability) while ensuring the desired water permeability in the porous substrate. In the present specification, “not having water permeability” means a measurement object (that is, an LDH dense film and / or an LDH dense film and / or an object when the water permeability is evaluated by a denseness determination test described in the next paragraph or a method or configuration according thereto. It means that the water contacted to one surface side of the porous substrate) does not permeate the other surface side. In the present invention, the average pore diameter can be measured by measuring the longest distance of the pores based on the electron microscope image of the surface of the porous substrate. The magnification of the electron microscope image used for this measurement is 20000 times or more, and all obtained pore diameters are arranged in the order of size, and the upper 15 points and the lower 15 points from the average value. The average pore size can be obtained by calculating the average value of minutes. For the length measurement, a length measurement function of SEM software, image analysis software (for example, Photoshop, manufactured by Adobe) or the like can be used.

  In addition, an example of the procedure of the denseness determination test for confirming that the film sample has a denseness that does not have water permeability is as follows. First, as shown in FIG. 15A, a composite material sample (that is, an LDH dense film and / or a porous substrate) 120 (cut into a 1 cm × 1 cm square) 120 cm in the center is 0.5 cm × Silicone rubber 122 having a 0.5 cm square opening 122a is bonded, and the resulting laminate is bonded between two acrylic containers 124 and 126. The bottom of the acrylic container 124 disposed on the silicon rubber 122 side is pulled out, whereby the silicon rubber 122 is bonded to the acrylic container 124 with the opening 122a open. On the other hand, the acrylic container 126 disposed on the porous substrate side of the composite material sample 120 has a bottom, and ion-exchanged water 128 is contained in the container 126. That is, by assembling the components upside down after assembly, the constituent members are arranged so that the ion exchange water 128 is in contact with the porous substrate side of the composite material sample 120. After assembling these components, the total weight is measured. Needless to say, the container 126 has a closed vent hole (not shown) and is opened after being turned upside down. As shown in FIG. 15B, the assembly is placed upside down and held at 25 ° C. for 1 week, after which the total weight is measured again. At this time, if water droplets adhere to the inner side surface of the acrylic container 124, the water droplets are wiped off. Then, the density is determined by calculating the difference in the total weight before and after the test. If no change is observed in the weight of the ion-exchanged water even after holding at 25 ° C. for 1 week, the membrane sample is judged to have high density so as not to have water permeability.

  The surface of the porous substrate preferably has a porosity of 10 to 60%, more preferably 15 to 55%, and still more preferably 20 to 50%. By setting it within these ranges, it is possible to form an LDH dense membrane that is so dense that it does not have water permeability (desirably water permeability and air permeability) while ensuring the desired water permeability in the porous substrate. Here, the porosity of the surface of the porous substrate is adopted because it is easy to measure the porosity using the image processing described below, and the porosity of the surface of the porous substrate. This is because it can be said that it generally represents the porosity inside the porous substrate. That is, if the surface of the porous substrate is dense, the inside of the porous substrate can be said to be dense as well. In the present invention, the porosity of the surface of the porous substrate can be measured as follows by a technique using image processing. That is, 1) An electron microscope (SEM) image of the surface of the porous substrate (acquisition of 10,000 times or more) is obtained, and 2) a grayscale SEM image is read using image analysis software such as Photoshop (manufactured by Adobe). 3) Create a black-and-white binary image by the procedure of [Image] → [Tonal Correction] → [Turn Tone], and 4) The value obtained by dividing the number of pixels occupied by the black part by the total number of pixels in the image Rate (%). The porosity measurement by this image processing is preferably performed for a 6 μm × 6 μm region on the surface of the porous substrate. In order to obtain a more objective index, three arbitrarily selected regions are used. It is more preferable to employ the average value of the obtained porosity.

(B) Hydrothermal treatment In this step (b), the substrate is subjected to hydrothermal treatment in a raw material aqueous solution containing the constituent elements of LDH to form an LDH dense film on the surface of the substrate. By passing through the step (a), the base material exhibits a negative zeta potential in almost the entire pH range of 5 to 8. Therefore, a highly densified LDH dense film is evenly and uniformly distributed on the surface of the base material by the mechanism described above. Can be formed.

A preferable raw material aqueous solution contains magnesium ions (Mg ²⁺ ) and aluminum ions (Al ³⁺ ) at a predetermined total concentration, and contains urea. By the presence of urea, ammonia is generated in the solution by utilizing hydrolysis of urea, so that the pH value increases, and the coexisting metal ions form hydroxides to obtain LDH. Further, since carbon dioxide is generated in the hydrolysis, LDH in which the anion is carbonate ion type can be obtained. The total concentration (Mg ²⁺ + Al ³⁺ ) of magnesium ions and aluminum ions contained in the raw material aqueous solution is preferably 0.20 to 0.40 mol / L, more preferably 0.22 to 0.38 mol / L, still more preferably 0.24 to 0.36 mol / L, particularly preferably 0.26 to 0.34 mol / L. When the concentration is within such a range, nucleation and crystal growth can proceed in a balanced manner, and an LDH dense film excellent not only in orientation but also in denseness can be obtained. That is, when the total concentration of magnesium ions and aluminum ions is low, crystal growth becomes dominant compared to nucleation, and the number of particles decreases and particle size increases. It is considered that the generation becomes dominant, the number of particles increases, and the particle size decreases.

Preferably, magnesium nitrate and aluminum nitrate are dissolved in the raw material aqueous solution, so that the raw material aqueous solution contains nitrate ions in addition to magnesium ions and aluminum ions. In this case, the molar ratio (urea / NO ₃ ⁻ ) of urea to nitrate ions (NO ₃ ⁻ ) in the raw material aqueous solution is preferably 2 to 6, and more preferably 4 to 5.

  The substrate may be immersed in the raw material aqueous solution in a desired direction (for example, horizontally or vertically). When the substrate is held horizontally, it is only necessary to suspend, float, or place the substrate so as to contact the bottom of the container. For example, the substrate may be fixed in a state of floating in the raw material aqueous solution from the bottom of the container. . In the case where the substrate is held vertically, a jig that can vertically set the substrate may be placed on the bottom of the container. In any case, the LDH is substantially perpendicular to or close to the substrate (ie, the direction in which the LDH plate-like particles intersect the surface of the substrate (substrate surface) substantially perpendicularly or obliquely). It is preferable to adopt a configuration or arrangement that allows growth to (i).

  In the raw material aqueous solution, the substrate is subjected to hydrothermal treatment to form an LDH dense film on the surface of the substrate. This hydrothermal treatment is preferably carried out in a sealed container (preferably an autoclave) at 60 to 150 ° C., more preferably 65 to 120 ° C., further preferably 65 to 100 ° C., particularly preferably 70 to 90 ° C. The upper limit temperature of the hydrothermal treatment may be selected so that the base material (for example, the polymer base material) is not deformed by heat. The rate of temperature increase during the hydrothermal treatment is not particularly limited and may be, for example, 10 to 200 ° C./h, preferably 100 to 200 ° C./h, more preferably 100 to 150 ° C./h. The hydrothermal treatment time may be appropriately determined according to the target density and thickness of the LDH dense film.

  After the hydrothermal treatment, the substrate is preferably taken out from the sealed container and washed with ion exchange water.

  The LDH dense film produced as described above is one in which LDH plate-like particles are highly densified and oriented in a substantially vertical direction advantageous for conduction. That is, the LDH dense film typically does not have water permeability (desirably, water permeability and air permeability) due to high density. Specifically, the LDH dense film preferably has a surface film density of 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 93% or more (measurement of surface film density). The method shall be described later). The LDH constituting the LDH dense film is composed of an aggregate of a plurality of plate-like particles, and the plurality of plate-like particles are oriented so that their plate surfaces intersect the surface of the substrate substantially perpendicularly or obliquely. Typically, it is oriented in the direction. Therefore, when a dense LDH film having sufficient gas tightness is used for a battery such as a zinc-air battery, an improvement in power generation performance can be expected, and a secondary of a zinc-air battery using an electrolytic solution that has not been conventionally applicable can be expected. It is expected to be applied to new separators for zinc dendrite progress prevention and carbon dioxide invasion prevention, which have become a major barrier to battery use. Similarly, it is expected to be applied to a nickel-zinc battery in which the progress of zinc dendrite is a major barrier to practical use.

  By the way, the LDH dense film obtained by the manufacturing method can be formed on both surfaces of the substrate. For this reason, in order to form an LDH dense film on a porous substrate and to make it suitable for use as a separator, the LDH dense film on one side of the porous substrate is mechanically shaved after film formation, Alternatively, it is desirable to take measures so that an LDH dense film cannot be formed on one surface during film formation.

LDH dense film and LDH-containing composite material The method of the present invention can be used to produce an LDH dense film and an LDH-containing composite material comprising the LDH dense film. An LDH-containing composite material according to a preferred embodiment of the present invention includes a porous substrate and a functional layer (typically an LDH dense film) formed on and / or in the porous substrate. It becomes. The functional layer has a general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · mH ₂ O (wherein M ²⁺ is a divalent cation and M ³⁺ is a trivalent cation) A ⁿ⁻ is an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4), and includes a layered double hydroxide (LDH). (Preferably water permeability and breathability). That is, the porous material can have water permeability due to the presence of pores, but the functional layer is typically densified with LDH to such an extent that it does not have water permeability. The functional layer is preferably formed on a porous substrate. For example, as shown in FIG. 1, in the LDH-containing composite material 10, the functional layer 14 is preferably formed on the porous substrate 12 as an LDH dense film. In this case, needless to say, LDH may be formed on the surface of the porous substrate 12 and in the pores in the vicinity thereof as shown in FIG. 1 due to the nature of the porous substrate 12. Alternatively, as in the LDH composite material 10 ′ shown in FIG. 2, LDH is densely formed in the porous substrate 12 (for example, in the surface of the porous substrate 12 and in the pores in the vicinity thereof). At least a part of the substrate 12 may constitute the functional layer 14 ′. In this regard, the composite material 10 ′ shown in FIG. 2 has a structure in which the film-corresponding portion in the functional layer 14 of the composite material 10 shown in FIG. It suffices if the functional layer exists in parallel with the surface. In any case, in the LDH-containing composite material of this embodiment, since the functional layer is densified with LDH to such an extent that it does not have water permeability, it has a unique characteristic of having hydroxide ion conductivity but not water permeability. Can have functions.

  As described above, in the LDH-containing composite material of this aspect, the function is so dense that it does not have water permeability (preferably water permeability and air permeability) despite the use of a porous substrate that can have water permeability. A layer is formed. As a result, the LDH-containing composite material of the present embodiment as a whole has hydroxide ion conductivity but does not have water permeability, and can exhibit a function as a battery separator. As described above, when considering application of LDH as a solid electrolyte separator for a battery, there was a problem that a bulk LDH dense body had high resistance, but in the composite material of this embodiment, a porous substrate is used. Since strength can be imparted, the LDH-containing functional layer can be thinned to reduce resistance. In addition, since the porous substrate can have water permeability, the electrolyte can reach the LDH-containing functional layer when used as a solid electrolyte separator for a battery. That is, the LDH-containing composite material of this embodiment is extremely useful as a solid electrolyte separator applicable to various battery applications such as metal-air batteries (for example, zinc-air batteries) and other various zinc secondary batteries (for example, nickel-zinc batteries). Can be a material.

The functional layer in the composite material of this embodiment has a general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · mH ₂ O (wherein M ²⁺ is a divalent cation, M ³⁺ is a trivalent ^{cation, a n-n-valent} anion, n is an integer of 1 or more, layered double hydroxides x is represented by a is) 0.1 to 0.4 (LDH) It does not have water permeability. In the above general formula, M ²⁺ may be any divalent cation, and preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ may be any trivalent cation, but preferred examples include Al ³⁺ or Cr ³⁺ , and more preferred is Al ³⁺ . A ^n- may be any anion, preferred examples OH ^- and _CO ^{3 2-} and the like. Accordingly, the general formula is an ^{Mg 2+} at least ^{M 2+,} include ^{Al 3+} in ^{M 3+,} to ^{A n-OH -} and / or _CO preferably contains ^{3 2-.} n is an integer of 1 or more, preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is an arbitrary real number.

  The functional layer is formed on the porous substrate and / or in the porous substrate, preferably on the porous substrate. For example, when the functional layer 14 is formed on the porous substrate 12 as shown in FIG. 1, the functional layer 14 is in the form of an LDH dense film, which is typically formed from LDH. Become. Further, when the functional layer 14 ′ is formed in the porous substrate 12 as shown in FIG. 2, the surface of the porous substrate 12 (typically the surface of the porous substrate 12 and the vicinity thereof). Since the LDH is densely formed in the pores), the functional layer 14 ′ is typically composed of at least a part of the porous substrate 12 and LDH. The composite material 10 ′ and the functional layer 14 ′ shown in FIG. 2 can be obtained by removing a portion corresponding to the film in the functional layer 14 from the composite material 10 shown in FIG. 1 by a known method such as polishing or cutting. .

  The functional layer does not have water permeability (preferably water permeability and air permeability). For example, the functional layer does not allow water to pass through even if one side of the functional layer is contacted with water at 25 ° C. for one week. That is, the functional layer is densified with LDH to such an extent that it does not have water permeability. However, when a defect having water permeability locally and / or accidentally exists in the functional film, water impermeableness can be improved by filling the defect with an appropriate repair agent (for example, epoxy resin) and repairing the defect. Such a repair agent need not necessarily have hydroxide ion conductivity. In any case, the surface of the functional layer (typically the LDH dense film) preferably has a porosity of 20% or less, more preferably 15% or less, still more preferably 10% or less, particularly preferably 7%. It is as follows. In other words, the functional layer (typically the LDH dense film) preferably has a surface film density of 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 93% or more. is there. It means that the lower the porosity of the surface of the functional layer, the higher the density of the functional layer (typically the LDH dense film), which is preferable. The dense functional layer is useful as a hydroxide ion conductor in applications such as functional membranes such as battery separators (eg, hydroxide ion conductive separators for zinc-air batteries). Here, the porosity of the surface of the functional layer is used because it is easy to measure the porosity using the image processing described below. It is because it can be said that the porosity of is generally expressed. That is, if the surface of the functional layer is dense, the inside of the functional layer can be said to be dense as well. In this embodiment, the porosity and surface film density on the surface of the functional layer can be measured as follows by a technique using image processing. That is, 1) an electron microscope (SEM) image of the surface of the functional layer (magnification of 10,000 times or more) is acquired, and 2) a grayscale SEM image is read using image analysis software such as Photoshop (manufactured by Adobe). ) Create a black-and-white binary image by the procedure of [Image] → [Tone Correction] → [2 Gradation], and 4) Porosity (the value obtained by dividing the number of pixels occupied by the black part by the total number of pixels in the image) %). Note that the porosity measurement by this image processing is preferably performed for a 6 μm × 6 μm region on the surface of the functional layer. In order to obtain a more objective index, the porosity is obtained for three regions selected arbitrarily. It is more preferable to adopt the average value of the porosity. Further, by using the porosity of the film surface, the density D when viewed from the film surface (hereinafter referred to as surface film density) can be calculated by D = 100% − (porosity of the film surface).

  The layered double hydroxide is composed of an aggregate of a plurality of plate-like particles (that is, LDH plate-like particles), and the plurality of plate-like particles are substantially the same as the surface of the porous substrate (substrate surface). It is preferably oriented in a direction that intersects perpendicularly or diagonally. As shown in FIG. 1, this embodiment is an embodiment that can be realized particularly preferably when the LDH-containing composite material 10 is formed on the porous substrate 12 as the functional layer 14 as an LDH dense film. As in the LDH composite material 10 ′ shown in FIG. 2, LDH is densely formed in the porous substrate 12 (typically in the surface of the porous substrate 12 and in the pores in the vicinity thereof). This can be realized even when at least a part of the substrate 12 forms the functional layer 14 '.

That is, the LDH crystal is known to have the form of a plate-like particle having a layered structure as shown in FIG. 3, but the above-mentioned substantially vertical or oblique orientation has an LDH-containing functional layer (for example, an LDH dense film). This is a very advantageous property. This is because an oriented LDH-containing functional layer (eg, an oriented LDH dense film) has a hydroxide ion conductivity perpendicular to this in the direction in which the LDH plate-like particles are oriented (ie, in a direction parallel to the LDH layer). This is because there is a conductivity anisotropy that is much higher than the conductivity in the direction. In fact, the present inventors have found that in an LDH oriented bulk body, the conductivity (S / cm) in the orientation direction is an order of magnitude higher than the conductivity (S / cm) in the direction perpendicular to the orientation direction. It has gained. That is, the substantially vertical or oblique orientation in the LDH-containing functional layer of the present embodiment indicates the conductivity anisotropy that the LDH oriented body can have in the layer thickness direction (that is, the direction perpendicular to the surface of the functional layer or the porous substrate). As a result, the conductivity in the layer thickness direction can be maximized or significantly increased. In addition, since the LDH-containing functional layer has a layer form, lower resistance than that of the bulk form LDH can be realized. The LDH-containing functional layer having such an orientation is easy to conduct hydroxide ions in the layer thickness direction. In addition, since it is densified, it is extremely suitable for use in functional membranes such as battery separators (eg, hydroxide ion conductive separators for zinc-air batteries) where high conductivity in the layer thickness direction and denseness are desired. Suitable.

  Particularly preferably, the LDH plate-like particles are highly oriented in a substantially vertical direction in the LDH-containing functional layer (typically an LDH dense film). This high degree of orientation is confirmed by the fact that when the surface of the functional layer is measured by the X-ray diffraction method, the peak of the (003) plane is not substantially detected or smaller than the peak of the (012) plane. (However, when a porous substrate in which a diffraction peak is observed at the same position as the peak due to the (012) plane is used, the peak of the (012) plane due to the LDH plate-like particle is used. This is not the case). This characteristic peak characteristic indicates that the LDH plate-like particles constituting the functional layer are oriented in a direction substantially perpendicular to the functional layer (that is, a vertical direction or an oblique direction similar thereto, preferably a vertical direction). In other words, the (003) plane peak is known as the strongest peak observed when X-ray diffraction is performed on non-oriented LDH powder. In an oriented LDH-containing functional layer, LDH plate-like particles function. By being oriented in a direction substantially perpendicular to the layer, the peak of the (003) plane is not substantially detected or detected smaller than the peak of the (012) plane. This is because the c-axis direction (00l) plane (l is 3 and 6) to which the (003) plane belongs is a plane parallel to the layered structure of the LDH plate-like particles. On the other hand, when oriented in a substantially vertical direction, the LDH layered structure also faces in the substantially vertical direction. As a result, when the surface of the functional layer is measured by X-ray diffraction, the (00l) plane (l is 3 and 6). This is because the peak of) does not appear or becomes difficult to appear. In particular, the peak of the (003) plane tends to be stronger than the peak of the (006) plane when it is present. I can say that. Therefore, in the oriented LDH-containing functional layer, the (003) plane peak is substantially not detected or smaller than the (012) plane peak, suggesting a high degree of vertical orientation. It can be said that it is preferable. In this regard, the LDH alignment films disclosed in Patent Documents 1 and 2 and Non-Patent Document 1 are those in which the peak of the (003) plane is detected strongly, and are considered to be inferior in alignment in the substantially vertical direction. Moreover, it seems that it does not have high density.

  The functional layer preferably has a thickness of 100 μm or less, more preferably 75 μm or less, still more preferably 50 μm or less, particularly preferably 25 μm or less, and most preferably 5 μm or less. Such thinness can reduce the resistance of the functional layer. The functional layer is preferably formed as an LDH dense film on the porous substrate, and in this case, the thickness of the functional layer corresponds to the thickness of the LDH dense film. Further, when the functional layer is formed in the porous substrate, the thickness of the functional layer corresponds to the thickness of the composite layer composed of at least part of the porous substrate and LDH, and the functional layer is porous. When formed over and in the substrate, this corresponds to the total thickness of the LDH dense film and the composite layer. In any case, when the thickness is as described above, a desired low resistance suitable for practical use in battery applications and the like can be realized. The lower limit of the thickness of the LDH alignment film is not particularly limited because it varies depending on the application, but in order to ensure a certain degree of hardness desired as a functional film such as a separator, the thickness is preferably 1 μm or more. Preferably it is 2 micrometers or more.

  The present invention is more specifically described by the following examples.

Examples A1 to A5
Hereinafter, an example in which a layered double hydroxide alignment film is prepared on a substrate will be described. In the following examples, the evaluation method of the substrate or the film sample was as follows.

Evaluation 1 : Zeta potential measurement The zeta potential of the substrate was measured at room temperature using a zeta potential measurement system (ELS-Z manufactured by Otsuka Electronics Co., Ltd.). Specifically, a substrate (15 mm × 15 mm × 35 mm) is set in a plate sample cell, and measured by electrophoresis using a 10 mM NaCl aqueous solution in which several drops of standard monitor particles manufactured by Otsuka Electronics Co., Ltd. are dispersed. did. The value when the pH was changed from 3 to 11 by 1 with a pH titrator was measured.

Evaluation 2 : Identification of the film sample The crystal phase of the film sample was measured with an X-ray diffractometer (RINT TTR III manufactured by Rigaku Corporation) under the measurement conditions of voltage: 50 kV, current value: 300 mA, measurement range: 10 to 70 °. To obtain an XRD profile. About the obtained XRD profile, JCPDS card NO. Identification was performed using a diffraction peak of a layered double hydroxide (hydrotalcite compound) described in 35-0964.

Evaluation 3 : Observation of microstructure The surface microstructure of the film sample was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 kV.

Evaluation 4 : Measurement of Porosity and Membrane Density For the membrane sample, the porosity of the membrane surface was measured by a technique using image processing. The porosity is measured by 1) obtaining an electron microscope (SEM) image (magnification of 10,000 times or more) of the surface of the membrane according to the procedure shown in Evaluation 2, and 2) using image analysis software such as Photoshop (manufactured by Adobe). 3) Read a grayscale SEM image, and 3) Create a black and white binary image by the procedure of [Image] → [Tone correction] → [2 gradation]. 4) The number of pixels occupied by the black part The value divided by the total number of pixels was used as the porosity (%). This porosity measurement was performed on a 6 μm × 6 μm region of the membrane sample surface. Further, using the porosity of the film surface, the density D (hereinafter referred to as surface film density) when viewed from the film surface was calculated by D = 100% − (porosity of the film surface). Based on the measured film density on the surface, the film density was evaluated in the following two stages.
<Evaluation criteria for compactness>
A: Surface film density is 80% or more B: Surface film density is less than 80%

Examples A1 and A2 : Example using a polystyrene base material (1) Preparation of base material A polystyrene plate (26.5 mm × 30 mm × 1.845 mm) was prepared as a base material and wiped and washed with ethanol. In Example A1, the zeta potential of the washed substrate was measured by the method described in Evaluation 1 above, and the result shown in FIG. 5 was obtained.

(2) Sulfonation treatment (implemented only in Example A2)
In Example A2, the washed polystyrene plate was further sulfonated. Specifically, the polystyrene plate was immersed in a commercially available concentrated sulfuric acid (manufactured by Kanto Chemical Co., Inc., content 95.0% or more) in a sealed container at room temperature. After immersion for 12 days, the polystyrene plate was taken out from the concentrated sulfuric acid, washed with ion-exchanged water, and dried at 40 ° C. for 6 hours. When the zeta potential of the base material of Example A2 prepared in this way was measured by the method described in Evaluation 1 above, the result shown in FIG. 5 was obtained.

(3) As the manufacturing raw material of the raw aqueous solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate (Al _{(NO 3)} 3 · 9H ₂ O, manufactured by Kanto Chemical Co., Inc.) and urea ((NH 2) 2 CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate so that the cation ratio (Mg ²⁺ / Al ³⁺ ) is 2 and the total metal ion molarity (Mg ²⁺ + Al ³⁺ ) is 0.280 mol / L. In a beaker, ion exchange water was added to make a total volume of 75 ml. After stirring the obtained solution, urea weighed at a ratio of urea / NO ³ = 4 was added to the solution and further stirred to obtain a raw material aqueous solution.

(4) Film formation by hydrothermal treatment A Teflon (registered trademark) sealed container (with an internal volume of 100 ml, the outside is a stainless steel jacket) and the raw material aqueous solution prepared in (3) above and the substrate washed in (1) above (example) A1) or the substrate sulfonated in (2) above (Example A2) was encapsulated. At this time, the base material is naturally floating in the solution. Thereafter, a hydrothermal treatment was performed at a hydrothermal temperature of 70 ° C. for 168 hours (7 days) to form a layered double hydroxide alignment film (functional layer) on the substrate surface. After 168 hours, the substrate was taken out from the sealed container and washed with ion-exchanged water to obtain a layered double hydroxide film on the substrate. The thickness of the obtained film sample was about 2.0 μm.

(5) Evaluation result Evaluation 2-4 was performed with respect to the obtained LDH sample. The results are shown below together with the result of Evaluation 1.
-Evaluation 1: As shown in FIG. 5, the sulfonated polystyrene substrate of Example A2 is negatively charged by the sulfonic acid group on the surface as compared to the unsulfonated polystyrene substrate of Example A1, and the zeta It turned out that the electric potential fell overall. Specifically, the zeta potential over substantially the entire pH range of 3 to 8 was mostly positive for the base material of Example A1, but negative for the base material of Example A2. The non-sulfonated Example A1 polystyrene substrate was positively charged in most pH regions, suggesting that it is difficult to attach LDH.
-Evaluation 2: From the XRD profile, it was identified that the film sample was LDH (hydrotalcite compound).
-Evaluation 3: The SEM image of the surface microstructure of the film sample was as shown in FIG. Almost no LDH was formed on the polystyrene substrate of Example A1 which was not sulfonated, but a dense LDH film was formed on the polystyrene substrate of Example A2 which was sulfonated and had a strong negative zeta potential and was negatively charged. Obtained.
-Evaluation 4: Regarding the evaluation of the denseness based on the surface film density on the surface of the film sample, Example A1 was Evaluation B and Example A2 was Evaluation A.

Examples A3 and A4: zirconia (3YSZ) example using a base material (1) Zirconia group prepared 2cm square of substrate material _{(3YSZ, Y 2 O 3:} 3mol%) was prepared. The obtained base material (2 cm square) was put into a beaker, ultrasonically washed in 25 ml of acetone for 5 minutes, ultrasonically washed in 25 ml of ethanol for 2 minutes, and then ultrasonically washed in 25 ml of ion-exchanged water for 1 minute.

(2) Preparation of surfactant (implemented only in Example A4)
In Example A4, a commercially available anionic surfactant solution (Naphthalenesulfonic acid Na formalin condensate, demole SS-L, manufactured by Kao Corporation) and ion-exchanged water and (surfactant solution): (ion-exchanged water) ) Was mixed at a weight ratio of 2: 100 to prepare a diluted surfactant solution for use in the surfactant treatment of the substrate.

(3) Treatment with surfactant (implemented only in Example A4)
In Example A4, the substrates cleaned in (1) above were placed in a beaker containing 25 ml of the diluted surfactant solution so as not to contact each other together with the rotor, and stirred at 500 rpm on a hot stirrer. The film was immersed for 1 day at a temperature of 40 ° C.

(4) As the manufacturing raw material of the raw aqueous solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate _{(Al (NO 3) 3 ·} 9H ₂ O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate so that the cation ratio (Mg ²⁺ / Al ³⁺ ) is 2 and the total metal ion molar concentration (Mg ²⁺ + Al ³⁺ ) is 0.320 mol / L. In a beaker, ion exchange water was added to make a total volume of 75 ml. After stirring the obtained solution, urea weighed at a ratio of urea / NO ₃ ⁻ = 4 was added to the solution, and further stirred to obtain a raw material aqueous solution.

(5) Film formation by hydrothermal treatment A Teflon (registered trademark) sealed container (with an internal volume of 100 ml, the outside is a stainless steel jacket) and the raw material aqueous solution prepared in (4) above and the substrate washed in (1) above (example) A3) or the substrate treated with the surfactant in (3) above (Example A4) was encapsulated. At this time, the base material was fixed by being floated from the bottom of a Teflon (registered trademark) sealed container, and placed horizontally so that the solution was in contact with both surfaces of the base material. Thereafter, a hydrothermal treatment was performed at a hydrothermal temperature of 70 ° C. for 168 hours (7 days) to form a layered double hydroxide alignment film (functional layer) on the substrate surface. After 168 hours, the substrate was taken out from the sealed container and washed with ion-exchanged water to obtain a layered double hydroxide film on the substrate.

(6) Evaluation results Evaluations 2 to 4 were performed on the obtained LDH film samples. The results are shown below together with the result of Evaluation 1.
-Evaluation 1: As shown in FIG. 6, the zeta potential in substantially the entire region of pH 5 to 8 was negative in both the base materials of Examples A3 and A4, but the base material of Example A3 not treated with the surfactant From the comparison with the surfactant-treated example A4 substrate, it was found that the zeta potential was lowered by treating the dense 3YSZ substrate with an anionic surfactant. It was suggested that the substrate of Example A4 treated with the surfactant is more likely to have LDH as compared to the substrate of Example A3 not treated with the surfactant.
-Evaluation 2: From the XRD profile, it was identified that both of the film samples of Examples A3 and A4 were LDH (hydrotalcite compound).
-Evaluation 3: The SEM image of the surface microstructure of the film sample was as shown in FIG. In Example A4, a dense 3YSZ substrate was treated with a surfactant to form an LDH film entirely. Since the 3YSZ base material without pretreatment of Example A3 was also negatively charged, LDH was generated to some extent (the density was high to some extent), but the density was lower than that of Example A4. By treating the dense 3YSZ substrate with a surfactant, it was more strongly negatively charged, so it was considered that LDH was easily attached.
-Evaluation 4: Evaluation of the denseness based on the surface film density on the surface of the film sample was Evaluation A in both Examples A3 and A4.

Example A5 : Example using titania porous substrate (1) Production of porous substrate Titania (manufactured by Ishihara Sangyo Co., Ltd., CR-EL), methylcellulose, and ion-exchanged water, (titania): (methylcellulose): After weighing so that the mass ratio of (ion-exchanged water) was 10: 1: 5, it was kneaded. The obtained kneaded product was subjected to extrusion molding using a hand press and molded into a size of 2.5 cm × 10 cm × thickness 0.5 cm. The obtained molded body was dried at 80 ° C. for 12 hours, then fired at 900 ° C. for 3 hours, and then processed into 2 cm × 2 cm × 0.3 cm to obtain a titania porous substrate.

  With respect to the obtained porous substrate, the porosity on the surface of the porous substrate was measured by a technique using image processing, and it was 46%. The porosity is measured by 1) observing the surface microstructure using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV, and an electron microscope on the surface of the porous substrate ( SEM) image (magnification of 10,000 times or more) is obtained, 2) a grayscale SEM image is read using image analysis software such as Photoshop (manufactured by Adobe), etc. 3) [Image] → [Tone Correction] → [2 A monochrome binary image was created by the procedure of [gradation], and 4) the porosity (%) was obtained by dividing the number of pixels occupied by the black portion by the total number of pixels in the image. This porosity measurement was performed on a 6 μm × 6 μm region on the surface of the porous substrate.

  Moreover, it was 0.5 micrometer when the average pore diameter of the porous base material was measured. In the present invention, the average pore diameter was measured by measuring the longest distance of the pores based on an electron microscope (SEM) image of the surface of the porous substrate. The magnification of the electron microscope (SEM) image used for this measurement is 20000 times, and all the obtained pore diameters are arranged in order of size, and the top 15 points and the bottom 15 points from the average value, and 30 points per visual field in total. The average value for two visual fields was calculated to obtain the average pore diameter. For length measurement, the length measurement function of SEM software was used.

  The obtained porous substrate was placed in a beaker, ultrasonically washed in 25 ml of acetone for 5 minutes, ultrasonically washed in 25 ml of ethanol for 2 minutes, and then ultrasonically washed in 25 ml of ion-exchanged water for 1 minute.

(2) Preparation raw material for the raw solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate _{(Al (NO 3) 3 ·} 9H ₂ O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate so that the cation ratio (Mg ²⁺ / Al ³⁺ ) is 2 and the total metal ion molar concentration (Mg ²⁺ + Al ³⁺ ) is 0.320 mol / L. In a beaker, ion exchange water was added to make a total volume of 75 ml. After stirring the obtained solution, urea weighed at a ratio of urea / NO ₃ ⁻ = 4 was added to the solution, and further stirred to obtain a raw material aqueous solution.

(3) Film formation by hydrothermal treatment A Teflon (registered trademark) sealed container (with an internal volume of 100 ml, the outside is a stainless steel jacket) and the raw material aqueous solution prepared in (2) above and the titania porous material washed in (1) above The substrate was encapsulated. At this time, the base material was fixed by being floated from the bottom of a Teflon (registered trademark) sealed container, and placed horizontally so that the solution was in contact with both surfaces of the base material. Thereafter, a hydrothermal treatment was performed at a hydrothermal temperature of 70 ° C. for 168 hours (7 days) to form a layered double hydroxide alignment film (functional layer) on the substrate surface. After 168 hours, the substrate was taken out from the sealed container and washed with ion-exchanged water to obtain a layered double hydroxide film on the substrate.

(4) Evaluation results Evaluations 2 to 4 were performed on the obtained LDH film samples. The results are shown below together with the result of Evaluation 1.
-Evaluation 1: As shown in FIG. 6, the porous titania substrate was positively charged in most pH regions like the polystyrene substrate of Example A1, and it was considered that LDH was not easily attached.
-Evaluation 2: From the XRD profile, it was identified that the sample was LDH (hydrotalcite compound).
-Evaluation 3: The SEM image of the surface microstructure of the film sample was as shown in FIG. Comparing Example A3 and Example A5 using a ceramic substrate without pretreatment, the dense 3YSZ substrate of Example A3 in which the zeta potential is more negatively charged is more porous titania substrate of Example A5 It was found that LDH is more easily attached (the substrate is less exposed). From this, it was suggested that the charge on the substrate surface affects the film formability of LDH. In particular, it is considered that the negative charge in the film forming process (for example, pH of about 5 to 8, in some cases changing to about 3 to 8) is effective in the film forming property of LDH.
-Evaluation 4: Evaluation of the density based on the surface film density on the surface of the film sample was evaluation B.

The results of Examples A1 to A5 are summarized in Table 1.

Examples B1-B4 (reference)
Hereinafter, an example in which a layered double hydroxide alignment film is produced on a nonporous substrate will be shown. These examples are positioned as reference examples in that the zeta potential of the substrate is not measured.

Example B1 (Reference): Preparation of layered double hydroxide alignment film (1) Sulfonation treatment of substrate As an aromatic polymer substrate capable of sulfonating the surface, 26.5 mm × 30.0 mm × 1.85 mm The polystyrene board of the dimension of was prepared. The surface of the polystyrene plate was wiped with ethanol and washed. This polystyrene plate was immersed in a commercially available concentrated sulfuric acid (manufactured by Kanto Chemical Co., Inc., concentration: 95.0% by mass or more) in a sealed container at room temperature. After the elapse of the immersion time shown in Table 2, the polystyrene plate was taken out from the concentrated sulfuric acid and washed with ion exchange water. The washed polystyrene plate was dried at 40 ° C. for 6 hours to obtain a polystyrene plate having a sulfonated surface as a base material for preparing Samples 1 to 17. Moreover, the polystyrene board which does not perform the said sulfonation process was also prepared as a base material in order to produce the sample 18 of a comparative example aspect.

Before and after the sulfonation treatment, the transmission spectrum of the polystyrene plate was measured by Fourier transform infrared spectroscopy (FT-IR) ATR method (Attenuated Total Reflection), and the sulfonic acid group-derived peak was measured. Detection was performed. This measurement was performed by using a horizontal ATR apparatus in the FT-IR apparatus and obtaining a transmission spectrum under the conditions of a measurement range of 4000 to 400 cm ⁻¹ with respect to the sample and the background, respectively, 64 times. FIG. 7 shows the transmission spectrum of the polystyrene plate subjected to sulfonation treatment in each concentrated sulfuric acid immersion time. As shown in FIG. 7, in the polystyrene plate subjected to the sulfonation treatment, a peak derived from a sulfonic acid group was confirmed at a wave number of 1127 cm ⁻¹ which does not appear in the plate not subjected to the sulfonation treatment, and the concentrated sulfuric acid immersion time was long. It can be seen that the size of the peak increases. Considering that the measurement area in each measurement is the same, it is considered that the amount (density) of the sulfonic acid group increases as the concentrated sulfuric acid immersion time increases. From the transmission spectrum obtained by the ATR method, derived from the sulfonic acid group of the transmittance peak value (T ₁₆₀₁ ) at ₁₆₀₁ cm ⁻¹ derived from phenyl group CC stretching (benzene ring skeleton) vibration, which does not change before and after the sulfonation treatment. The ratio (T ₁₆₀₁ / T ₁₁₂₇ ) to the transmittance peak value (T ₁₁₂₇ ) at ₁₁₂₇ cm ⁻¹ was calculated. The results are as shown in Table 2. It was suggested that the longer the concentrated sulfuric acid immersion time, the higher the ratio of sulfonic acid groups.

(2) Preparation raw material for the raw solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate _{(Al (NO 3) 3 ·} 9H ₂ O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in a beaker so that the cation ratio (Mg ²⁺ / Al ³⁺ ) and total metal ion molarity (Mg ²⁺ + Al ³⁺ ) shown in Table 3 are obtained. Then, ion exchange water was added thereto to make the total volume 75 ml. After stirring the obtained solution, urea weighed in the ratio shown in Table 3 was added to the solution and further stirred to obtain a raw material aqueous solution.

(3) Film formation by hydrothermal treatment A Teflon (registered trademark) sealed container (with an internal volume of 100 ml, the outside is a stainless steel jacket) and the sulfonated base prepared in (1) above and the raw material aqueous solution prepared in (2) above. Both materials were enclosed. At this time, the base material was naturally floated horizontally in the solution. Then, the layered double hydroxide alignment film was formed on the substrate surface by performing hydrothermal treatment under the conditions of hydrothermal temperature, hydrothermal time and heating rate shown in Table 3. After elapse of a predetermined time, the substrate is taken out from the sealed container, washed with ion-exchanged water, dried at 70 ° C. for 10 hours, and layered double hydroxide (hereinafter referred to as LDH) as samples 1 to 18 is formed on the substrate. I got it. Samples 1 to 17 had a film form, and the thickness thereof was about 2 μm. On the other hand, Sample 18 could not be formed.

Example B2 (Reference): Evaluation of orientation Samples 1 to 1 were measured with an X-ray diffractometer (D8 ADVANCE, manufactured by Bulker AXS) under the measurement conditions of voltage: 40 kV, current value: 40 mA, measurement range: 5-70 °. 18 crystal phases were measured. About the obtained XRD profile, JCPDS card NO. It identified using the diffraction peak of the layered double hydroxide (hydrotalcite compound) described in 35-0964. As a result, it was confirmed that Samples 1 to 17 were all layered double hydroxides (hydrotalcite compounds).

  Next, the degree of crystal orientation in the LDH film was evaluated based on the obtained XRD profile. For convenience of explanation, FIG. 8 shows the XRD profile obtained for the crystal phase of Sample 9 where the highest film density was obtained. The profile shown at the top of FIG. 8 corresponds to the crystal phase of the polystyrene substrate, the profile shown in the middle corresponds to the crystal phase of the polystyrene substrate with the LDH film, and the profile shown at the bottom is the LDH powder. Corresponds to the crystalline phase of. In the LDH powder, the peak of the (003) plane is the strongest line, but in the LDH alignment film, the peak of the (00l) plane (l is 3 and 6) is reduced, such as the (012) plane and the (110) plane. A peak was observed. From this, it was suggested that the peak of the (00l) plane could not be detected, so that the plate-like particles were oriented in a substantially vertical direction (that is, a vertical direction or an oblique direction similar thereto) with respect to the base material. .

The crystal orientation was evaluated for the other samples 1 to 8 and 10 to 18 in the same manner as for the sample 9 and evaluated in the following three stages. The results were as shown in Table 3.
<Evaluation criteria for crystal orientation>
A: (003) plane peak is not detected or (003) plane peak is less than half the size of (012) plane peak B: (003) plane peak is (012) plane peak C: The peak of the (003) plane is larger than the peak size of the (012) plane

Example B3 (Reference): Observation of microstructure The surface microstructure of Samples 1-6, 9-16, and 18 was measured using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10-20 kV. Observed. SEM images (secondary electron images) of the surface microstructures of the obtained samples 1 to 6, 9 to 16, and 18 are shown in FIGS. From the images shown in these figures, the sample with the smallest gap (that is, the highest density) was Sample 9. Further, Comparative Sample 18 did not have a film form.

  The cross-sectional microstructure of sample 9 was observed as follows. First, the microstructure of the broken section (hereinafter referred to as a broken section) of Sample 9 was observed with a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV. An SEM image of the fracture cross-sectional microstructure of Sample 9 obtained in this way is shown in FIG.

  Next, the fractured cross-section of the sample 9 is polished by FIB polishing or cryomilling to form a polished cross-section, and the microstructure of the polished cross-section is measured from 1.5 kV to 1.5 kV using a field emission scanning electron microscope (FE-SEM). Observation was made at an acceleration voltage of 3 kV. FIG. 13 shows an SEM image of the polished cross-sectional microstructure of Sample 9 obtained in this way. Further, when the microstructure of the polished cross section of sample 2 was observed in the same manner as described above, the SEM image shown in FIG. 14 was obtained.

Example B4 (Reference): Measurement of Porosity and Membrane Density For samples 1 to 6 and 9 to 16 and 18, the porosity of the membrane surface was measured by a technique using image processing. The porosity is measured by 1) acquiring an electron microscope (SEM) image (magnification of 10,000 times or more) of the surface of the membrane according to the procedure shown in Example B3, and 2) using image analysis software such as Photoshop (manufactured by Adobe). 3) Read the grayscale SEM image, and 3) Create a monochrome binary image by adjusting the threshold value of the histogram in the order of [Image] → [Tone correction] → [2 gradation] 4) The value obtained by dividing the number of pixels occupied by the black portion by the total number of pixels in the image was taken as the porosity (%). This porosity measurement was performed on a 6 μm × 6 μm region of the alignment film surface.

Moreover, when the density D when viewed from the film surface (hereinafter referred to as surface film density) was calculated by D = 100% − (porosity of the film surface) using the porosity of the obtained film surface, The results shown in Table 3 were obtained. Further, when the film density was evaluated based on the measured film density of the surface in the following four stages, it was as shown in Table 3.
<Evaluation criteria for compactness>
A: Surface film density is 90% or more B: Surface film density is 80% or more and less than 90% C: Surface film density is 50% or more and less than 80% D: Surface film density is less than 50%

  For samples 2 and 9, the porosity of the polished cross section was also measured. The porosity of this polished cross section is also measured by the above-described film surface except that an electron microscope (SEM) image (magnification of 10,000 times or more) of the cross-section polished surface in the thickness direction of the film was obtained according to the procedure shown in Example B3. This was carried out in the same manner as the porosity. This porosity measurement was performed on a 2 μm × 4 μm region of the alignment film cross section. Thus, the porosity calculated from the cross-sectional polished surface of Sample 9 was 4.8% on average (average value of two cross-sectional polished surfaces), and it was confirmed that a high-density film was formed. Further, the porosity of the polished cross section of Sample 2 having a density lower than that of Sample 9 was calculated to be 22.9% on average (average value of two cross-section polished surfaces). As the results shown in Table 3, the surface porosity and the cross-sectional porosity generally correspond. From this, the above-mentioned surface film density calculated based on the surface porosity, and further, the evaluation of the film density based on the above-mentioned film density generally includes not only the film surface but also the characteristics of the entire film including the film thickness direction. You can see that it reflects.

  As shown in Table 3, in all of Samples 1 to 17, almost dense films having the desired crystal orientation were obtained. In particular, in Samples 5 to 10 in which the concentrated sulfuric acid immersion time was increased under the sulfonation treatment conditions to increase the amount (density) of the sulfone group, a film excellent in not only high crystal orientation but also denseness was obtained. On the other hand, in Sample 18 using a polystyrene substrate that was not sulfonated, LDH nuclei were not generated, and an LDH film was not formed.

10, 10 'LDH-containing composite material 12 Porous substrate 14, 14' Functional layer

Claims (14)

A method of forming a layered double hydroxide dense film on the surface of the substrate, the layered double hydroxide dense film, the general ^{_{formula: M 2+ 1-x M 3+}} x (OH) 2 A n- x / _n · _mH 2 O ^{(wherein, M 2+} is a divalent ^{cation, M 3+} is a trivalent ^{cation, a n-n-valent} anion, n represents an integer of 1 or more, x is 0. 1 to 0.4), and a layered double hydroxide represented by
(A) a step of preparing a substrate exhibiting a negative zeta potential in a substantially entire range of pH 5 to 8,
(B) in a raw material aqueous solution containing the constituent element of the layered double hydroxide, the substrate is hydrothermally treated to form the layered double hydroxide dense film on the surface of the substrate;
Including a method.   The method according to claim 1, wherein in the step (a), the substrate exhibits the negative zeta potential as an intrinsic property.   The step (a) comprises (a1) preparing a substrate exhibiting a positive zeta potential in at least a part of the pH range of pH 5 to 8, and (a2) the surface of the substrate having a pH of 5 to 5. A surface treatment so as to exhibit a negative zeta potential in substantially the entire region of 8.   The surface treatment in the step (a2) includes sulfonating the surface of the base material, treating the surface of the base material with a surfactant, treating the surface of the base material with plasma, and the base material. The method according to claim 3, wherein the method is carried out by at least one selected from the group consisting of treating the surface with acid or alkali.   The method according to any one of claims 1 to 4, wherein the hydrothermal treatment in the step (b) is performed at 60 to 150 ° C in a sealed container. In the general ^{formula, M 2+} comprises ^{Mg 2+,} include ^{M 3+} is ^{Al 3+, A n-is} OH ^- and / or _CO containing ^{3 2-,} according to any one of claims 1 to 5 Method. The raw material aqueous solution used in the step (b) contains magnesium ions (Mg ²⁺ ) and aluminum ions (Al ³⁺ ) at a total concentration of 0.20 to 0.40 mol / L, and contains urea. The method according to any one of claims 1 to 6.   The method according to claim 7, wherein magnesium nitrate and aluminum nitrate are dissolved in the raw material aqueous solution used in the step (b), so that the raw material aqueous solution contains nitrate ions in addition to magnesium ions and aluminum ions. The method according to claim 8, wherein a molar ratio of the urea to the nitrate ion (NO ₃ ⁻ ) in the raw material aqueous solution used in the step (b) is 4 to 5.   The method according to any one of claims 1 to 9, wherein the substrate is composed of at least one selected from the group consisting of a ceramic material, a metal material, and a polymer material.   The base material is a ceramic material, and the ceramic material is made of alumina, zirconia, titania, magnesia, spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, aluminum nitride, and silicon nitride. The method according to claim 10, wherein the method is at least one selected from the group.   The method according to claim 1, wherein the substrate is a porous substrate.   The layered double hydroxide constituting the layered double hydroxide dense membrane is composed of an aggregate of a plurality of plate-like particles, and the plate-like particles have their plate surfaces substantially perpendicular to the surface of the substrate. The method according to any one of claims 1 to 12, which is oriented in such a direction as to cross each other diagonally or diagonally.   The method according to claim 1, wherein the layered double hydroxide dense film has a surface film density of 80% or more.