JP7479673B2 - Hydrotalcite nanoparticles and hydrotalcite compositions - Google Patents

Description

The present invention relates to hydrotalcite nanoparticles and hydrotalcite compositions.

When oral bacteria accumulate on the teeth and form dental plaque, the bacteria inflame the gums and destroy the epithelial attachment between the teeth and gums, forming periodontal pockets, at the bottom of which periodontal pathogenic gram-negative anaerobic bacteria are present. Sulfur-containing amino acids in the oral cavity, such as methionine and cysteine, are broken down, generating volatile sulfur compounds (VSCs) such as hydrogen sulfide, methyl mercaptan, and dimethyl sulfide. Volatile sulfur compounds (VSCs) have a strong repellent effect and are indicators of bad breath. Furthermore, when the concentration of volatile sulfur compounds (VSCs) becomes high, it can cause destruction of gingival tissue, worsening of periodontal disease, recurrence of cavities, and blackening of prosthetic materials used in cavities treatment.

For this reason, reducing the concentration of volatile sulfur compounds (VSCs) in the oral cavity and improving periodontal pockets is effective in improving bad breath, but there are no commercially available materials that can adsorb and remove volatile sulfur compounds (VSCs). For this reason, there is a high demand for materials that can adsorb and deodorize volatile sulfur compounds (VSCs). For example, Patent Document 1 reports that a mixture of hydroxylamine sulfate, an organic hydrazide compound, zinc oxide, and smectite, which contains hydrotalcite, has the ability to adsorb hydrogen sulfide (deodorizing properties).

Meanwhile, the hydrotalcite compound is a layered double hydroxide having an anion exchange function, and is represented, for example, by the general formula (1):
[M ₁ ²⁺ _1−x M ₂ ³⁺ _x (OH) ₂ ][(A ⁿ⁻ ) _{x / n} mH ₂ O] (1)
[In the formula, _M1 represents a divalent metal, _M2 represents a trivalent metal, 0<x<1, A ^n- represents an anion, n represents 1 or 2, and m represents an integer of 1 or more.]
It has a composition represented by the formula:

For example, hydrotalcite compounds employing zinc as _M1 are used as adsorbents in various situations.

There is also a report that volatile sulfur compounds (VSCs) in a liquid phase are adsorbed onto hydrotalcite as a breath freshener (see, for example, Patent Document 2). In this document, an example is disclosed in which Mg is selected as M ₁ ²⁺ .

Referring to Patent Document 1, there is a demand for adsorbents (which can also be considered deodorants) for volatile sulfur compounds such as hydrogen sulfide, but currently there are no highly adsorbent materials available.

On the other hand, Patent Document 2 introduces hydrotalcite that effectively adsorbs volatile sulfur compounds in water. However, this is hydrotalcite [Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ] that is further heated after synthesis. In this case, in order to adsorb volatile sulfur compounds in water, heat treatment at a high temperature of 500°C was also required to dissolve the layer structure.

In contrast, Patent Document 3 discloses a compound having the following composition formula:
[Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ][( _CO32- ⁾ _{x/ 2.mH2O} ]
It has been reported that a hydrotalcite compound having the above structure can adsorb volatile sulfur compounds in a liquid phase without heat treatment, and its application to mouth guards and the like is being investigated.

JP 2011-030967 A International Publication No. 2012/150459 JP 2015-193000 A

According to Patent Document 3, volatile sulfur compounds in a liquid phase can be well adsorbed without heat treatment. However, there is room for improvement in the adsorption performance of volatile sulfur compounds immediately after the start of adsorption. In particular, when used as an oral composition such as toothpaste, it is not practical to brush teeth for a long period of time, so the adsorption performance of volatile sulfur compounds immediately after the start of adsorption is important.

The present invention aims to solve the above problems by providing a material that can effectively adsorb volatile sulfur compounds in a liquid phase without performing heat treatment at high temperatures, and that has excellent adsorption performance for volatile sulfur compounds immediately after the start of adsorption.

As a result of intensive research conducted by the present inventors to achieve the above object, the present inventors have found that the above problem can be solved by adjusting the crystallite size of hydrotalcite nanoparticles containing a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions to 1 to 20 nm. The above-mentioned crystallite size can be adjusted to 1 to 20 nm by using a surfactant. Based on the above findings, the present inventors conducted further research and completed the present invention. That is, the present invention includes the following configurations.

Item 1. A liquid phase volatile sulfur compound adsorbent containing a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions, and containing hydrotalcite nanoparticles having a crystallite size of 1 to 20 nm.

Item 2. The hydrotalcite compound is represented by the general formula (1):
[Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ][(A ^n- ) _{x/n mH2O} ] (1)
[In the formula, 0<x<1. ^{A n-} represents an anion. n represents 1 or 2. m represents an integer of 1 or more.]
Item 2. The adsorbent for volatile sulfur compounds in a liquid phase according to item 1, having a composition represented by the formula:

Item 3. The liquid phase volatile sulfur compound adsorbent according to Item 2, wherein x is 0.2 to 0.6.

Item 4. The adsorbent for volatile sulfur compounds in a liquid phase according to any one of items 1 to 3, wherein the hydrotalcite nanoparticles have at least a peak in the particle size distribution where the maximum particle size is 0.30 to 0.45 μm and a peak in the particle size distribution where the maximum particle size is 7.50 to 12.00 μm.

Item 5. A volatile sulfur compound adsorbent in a liquid phase, comprising a hydrotalcite composition containing a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions, and a surfactant.

Item 6. The hydrotalcite compound is represented by the general formula (1):
[Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ][(A ^n- ) _{x/n mH2O} ] (1)
[In the formula, 0<x<1. ^{A n-} represents an anion. n represents 1 or 2. m represents an integer of 1 or more.]
Item 6. The adsorbent for volatile sulfur compounds in a liquid phase according to item 5, having a composition represented by the formula:

Item 7. The liquid phase volatile sulfur compound adsorbent according to item 5 or 6, wherein x is 0.2 to 0.6.

Item 8. The liquid phase volatile sulfur compound adsorbent according to any one of items 5 to 7, wherein the content of the hydrotalcite compound is 90.0 to 99.9 mass%, with the total amount of the hydrotalcite composition being 100 mass%.

Item 9. A breath odor remover containing the liquid phase volatile sulfur compound adsorbent described in any one of items 1 to 8.

Item 10. A method for producing an adsorbent for volatile sulfur compounds in a liquid phase according to any one of items 1 to 8, comprising the steps of:
A manufacturing method comprising a step of mixing an aqueous solution containing a zinc salt and an aluminum salt with an aqueous solution containing a surfactant.

Item 11. The method according to item 10, wherein the surfactant is an anionic surfactant and/or a cationic surfactant.

Item 12. The method according to item 10 or 11, wherein the aqueous solution containing the surfactant further contains an oxoacid salt.

Item 13. The method according to any one of items 10 to 12, wherein the pH is adjusted to 9 to 12 during the mixing step.

Item 14. The manufacturing method according to any one of items 10 to 13, further comprising a step of stirring the mixed aqueous solution after the mixing step.

Item 15. A method for adsorbing volatile sulfur compounds in a liquid phase, comprising:
A method comprising a step of contacting, in a liquid phase, volatile sulfur compounds in the liquid phase with the adsorbent for volatile sulfur compounds in the liquid phase according to any one of items 1 to 8.

Item 16. The method according to item 15, wherein the contact step is carried out at 0 to 50°C.

The present invention provides a material that can effectively adsorb volatile sulfur compounds in a liquid phase without performing heat treatment at high temperatures, and that has excellent adsorption performance for volatile sulfur compounds immediately after the start of adsorption.

1 shows powder X-ray diffraction patterns of product A of Comparative Example 1, product B of Example 1, and product C of Example 2. (a) Product A, (b) Product B, (c) Product C, and (d) Zinc aluminum carbonate hydroxide hydrate (ICDD #48-1023). 1 shows powder X-ray diffraction patterns of Product D of Reference Example 1, Product E of Reference Example 2, and Product F of Reference Example 3. (a) Product D, (b) Product E, (c) Product F, (d) Zincite (ICDD#36-1451). Hall Plots of Product A of Comparative Example 1 (top diagram), Product B of Example 1 (middle diagram), and Product C of Example 2 (bottom diagram) are shown. Hall Plots of Product D of Reference Example 1 (upper graph), Product E of Reference Example 2 (middle graph), and Product F of Reference Example 3 (lower graph) are shown. 1 shows an SEM image and an EDS profile of Product A of Comparative Example 1. 1 shows an SEM image and EDS profile of Product B of Example 1. 1 shows an SEM image and EDS profile of Product C of Example 2. 1 shows SEM images of Product D of Reference Example 1 (top), Product E of Reference Example 2 (middle), and Product F of Reference Example 3 (bottom). FT-IR spectra of product A of Comparative Example 1, product B of Example 1, and product C of Example 2 are shown. (a) Product A, (b) Product B, (c) Product C. FT-IR spectra of product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3 are shown. (a) Product D, (b) Product E, and (c) Product F. 1 shows the particle size distributions of Product A of Comparative Example 1 (top graph), Product B of Example 1 (middle graph), and Product C of Example 2 (bottom graph). The particle size distributions of Product D of Reference Example 1 (top graph), Product E of Reference Example 2 (middle graph), and Product F of Reference Example 3 (bottom graph) are shown. The change rate of sulfide concentration over time after adding Product A of Comparative Example 1, Product B of Example 1, and Product C of Example 2 is shown for a 15-fold diluted _H2S aqueous solution (upper graph) and a 10-fold diluted _H2S aqueous solution (lower graph). ◇No sample, △Product A, □Product B, ○Product C. The graph shows the change over time in H ₂ S water and headspace in a closed container and the sulfide concentration in each when a 15-fold diluted H ₂ S aqueous solution was used: (a) no sample, (b) product A, (c) product B, (d) product C, (e) product D, ◇H ₂ S water, □headspace. The graph shows the change over time in H ₂ S water and headspace in a closed container and the sulfide concentration in each when a 10-fold diluted H ₂ S aqueous solution was used: (a) no sample, (b) product A, (c) product B, (d) product C, (e) product D, ◇H ₂ S water, □headspace. Powder X-ray diffraction patterns of Product A of Comparative Example 1 (top), Product B of Example 1 (middle), and Product C of Example 2 (bottom) before and after the adsorption experiment in Test Example 6. (a) Before adsorption, (b) After adsorption, (c) Zinc aluminum carbonate hydroxide hydrate (ICDD#48-1023), (d) Si (ICDD#27-1402). Powder X-ray diffraction patterns of Product D of Reference Example 1 (top), Product E of Reference Example 2 (middle), and Product F of Reference Example 3 (bottom) before and after the adsorption experiment in Test Example 6. (a) Before adsorption, (b) After adsorption, (c) Zinc aluminum carbonate hydroxide hydrate (ICDD#48-1023), (d) Si (ICDD#27-1402). 1 shows an SEM image and an EDS profile of Product A of Comparative Example 1 after an adsorption experiment in Test Example 6. 1 shows an SEM image and an EDS profile of Product B in Example 1 after an adsorption experiment in Test Example 6. 1 shows an SEM image and an EDS profile of Product C of Example 2 after an adsorption experiment in Test Example 6. 1 shows an SEM image and an EDS profile of Product D of Reference Example 1 after an adsorption experiment in Test Example 6. 1 shows an SEM image and an EDS profile of Product E of Reference Example 2 after an adsorption experiment in Test Example 6. 1 shows an SEM image and an EDS profile of Product F of Reference Example 3 after an adsorption experiment in Test Example 6.

In this specification, "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist of." In addition, in this specification, when a numerical range is indicated as "A to B," it means A or more and B or less.

1. Hydrotalcite Nanoparticles and Hydrotalcite Composition The hydrotalcite nanoparticles of the present invention contain a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions, and have a crystallite size of 1 to 20 nm.

The hydrotalcite composition of the present invention also contains a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions, and a surfactant.

(1-1) Hydrotalcite Compounds Hydrotalcite compounds undergo intercalation due to anion exchange between layers. Anion exchange is a phenomenon in which, for example, by immersing a hydrotalcite compound in a solution containing anions, the hydrotalcite nano-compound releases the anions it possesses and takes in the anions in the solution. In addition, the anions can be released by heat-treating the hydrotalcite compound.

Hydrogen sulfide, a typical volatile sulfur compound (VSC), is
_H2S ⇔ H ^{++ HS-}
HS ^- ⇔H ^{++ S2-}
It dissociates according to.

Near neutrality, free H ₂ S and HS ^- account for most of the species. Hydrotalcite compounds adsorb HS ^- through exchange with interlayer anions, and adsorb free H ₂ S through exchange with interlayer water.

Although the mechanism by which sulfides are adsorbed onto hydrotalcite compounds has not been elucidated, previous research by the inventors has revealed that the amount of sulfides adsorbed onto hydrotalcite compounds depends on the affinity between the metal atoms that make up the host layer of the hydrotalcite compound and the sulfides. In addition, zinc is an element known as a chalcophile, which has the property of easily combining with sulfur, and has a high affinity for sulfides.

In addition to zinc, iron, copper, molybdenum, mercury, and lead are known to be metals that easily bind with sulfur, but the metal elements that can be used are limited when considering use in the oral cavity. Hydrotalcite compounds containing zinc are white, which is also aesthetically pleasing. Trivalent cations include iron and chromium, but because they are used in the oral cavity, they are limited to iron and aluminum. The valence of iron is difficult to control and it becomes discolored, but aluminum is white, and even if it does leach into the body, more than 99% of it is excreted, so there is no concern that it will meet the provisional tolerable weekly intake of 2 mg/kg body weight/week (JECFA).

For this reason, the hydrotalcite compound contained in the hydrotalcite nanoparticles and hydrotalcite composition of the present invention is represented by the general formula (1):
[Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ][(A ^n- ) _{x/n mH2O} ] (1)
[In the formula, 0<x<1. ^{A n-} represents an anion. n represents 1 or 2. m represents an integer of 1 or more (for example, an integer from 1 to 10).]
It is preferable that the composition is represented by the following formula:

This hydrotalcite compound preferably has a hydrotalcite structure in which a host layer composed of a positively charged octahedral layer represented by Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ and a guest layer composed of anions compensating for the positive charge and interlayer water represented by ( ^An- ) _{x/n.mH2O are} alternately laminated.

In this hydrotalcite compound, the molar ratio of zinc ions to aluminum ions (zinc ions/aluminum ions) is preferably 0.7 to 4, and more preferably 1.8 to 3, from the viewpoints of the volatile sulfur compound (VSC) adsorption rate and volatile sulfur compound (VSC) adsorption performance. In other words, x in general formula (1) is preferably 0.2 to 0.6, and more preferably 0.25 to 0.35.

In this hydrotalcite compound, the anion A ^n- of the guest layer can be any anion, for example, an oxoacid ion such as CO ₃ ^2- , NO ₃ ^- , SO ₄ ^2- , PO ₄ ^3- , or B ₂ O ₅ ^4- . In particular, anions with high electron density are stable between layers, and CO ₃ ^2- is the most stable.

In addition, when sodium carbonate is used as a precipitant, the hydrotalcite compound can leave carbonate ions CO ₃ ²⁻ as anions A ⁿ⁻ . In this case, the hydrotalcite compound is represented by the general formula (2):
[Zn2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ][(A ^n- ) _{y .} ( ^CO32- _{) z.mH2O} ] (2)
[In the formula, 0<x<1 and x=yn+2z. A ^n- represents an anion. n represents 1 or 2. m represents an integer of 1 or more (for example, an integer from 1 to 10).]
and the guest layer can be (A ^n- ) _y .(CO ₃ ^2- ) _{z.mH 2} O. In this case, when no anions other than carbonate ions are contained, that is, when y is 0, the guest layer can be (CO ₃ ^2- ) _x/ 2.mH ₂ O.

(1-2) Hydrotalcite Nanoparticles The hydrotalcite nanoparticles of the present invention contain the above-mentioned hydrotalcite compound. The hydrotalcite nanoparticles of the present invention may be composed of only the above-mentioned hydrotalcite compound, or may have various surface treatment agents attached to the surface of the above-mentioned hydrotalcite compound.

When various surface treatment agents are attached to the surface of the hydrotalcite compound, examples of the surface treatment agents include surfactants and coupling agents such as silane coupling agents.

Surfactants are amphiphilic molecules having hydrophilic and hydrophobic groups. As surfactants, any of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants can be used, and from the viewpoint of volatile sulfur compound (VSC) adsorption rate, volatile sulfur compound (VSC) adsorption performance, etc., anionic surfactants and/or cationic surfactants are preferred. Specifically, for example, fatty acids (saturated or unsaturated fatty acids) such as lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, sodium laurate, sodium myristate, sodium palmitate, sodium margaric acid, sodium stearate, sodium oleate, sodium linoleate, and sodium linolenate, or salts thereof (particularly metal salts such as alkali metal salts), alkyl ammonium salts (particularly tetraalkyl ammonium salts) such as hexadecyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dioctyl dimethyl ammonium chloride, and distearyl dimethyl ammonium chloride can be used. Fatty acids are obtained by hydrolysis of natural fats and oils such as beef tallow, coconut oil, and palm oil. In addition, fatty acid sodium salts obtained by saponifying and decomposing fatty acids with sodium hydroxide have long been used as soap. Furthermore, fatty acids or their salts with a relatively large number of carbon atoms in the alkyl group are suitable surfactants for particle miniaturization, and fatty acids or their salts with 8 or more carbon atoms (especially 10 to 30 carbon atoms) are particularly preferred as surfactants.

Examples of silane coupling agents include vinylalkoxysilanes (vinyltrimethoxysilane, vinyltriethoxysilane, etc.), alkylalkoxysilanes (methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane), etc.

The above surface treatment agents can be used alone or in combination of two or more. Among them, surfactants are preferred from the viewpoints of volatile sulfur compound (VSC) adsorption rate, volatile sulfur compound (VSC) adsorption performance, etc. For example, according to the manufacturing method described below, when synthesizing hydrotalcite nanoparticles, the surfactant covers the surface to form micelles, suppressing crystal growth, and small-sized hydrotalcite nanoparticles can be obtained. In other words, it is easy to adjust the crystallite size of the hydrotalcite nanoparticles of the present invention. As a result, the surface area can be improved, and the volatile sulfur compound (VSC) adsorption rate, especially in the early stage of adsorption, can be improved.

When the hydrotalcite nanoparticles of the present invention contain the above-mentioned surface treatment agent, the content of the hydrotalcite compound is preferably 90.0 to 99.9 mass%, and more preferably 95.0 to 99.8 mass%, based on 100 mass% of the total amount of the hydrotalcite nanoparticles of the present invention, from the viewpoints of volatile sulfur compound (VSC) adsorption speed, volatile sulfur compound (VSC) adsorption performance, etc.

The hydrotalcite nanoparticles of the present invention have a crystallite diameter of 1 to 20 nm, preferably 2 to 15 nm. It is difficult to synthesize hydrotalcite nanoparticles with a crystallite diameter of less than 1 nm. Furthermore, if the crystallite diameter exceeds 20 nm, the adsorption rate of volatile sulfur compounds (VSCs) is insufficient, especially in the initial stage of adsorption. The crystallite diameter of the hydrotalcite nanoparticles of the present invention is calculated by a Hall Plot from the half-width at each peak position in the X-ray diffraction diagram.

The hydrotalcite nanoparticles of the present invention preferably have at least a peak with a maximum particle diameter of 0.30 to 0.45 μm and a peak with a maximum particle diameter of 7.50 to 12.00 μm in the particle size distribution. This makes it easier to obtain hydrotalcite nanoparticles that are particularly excellent in volatile sulfur compound (VSC) adsorption speed, volatile sulfur compound (VSC) adsorption performance, etc.

(1-3) Hydrotalcite Composition The hydrotalcite nanoparticles of the present invention contain the above-mentioned hydrotalcite compound and a surfactant.

Surfactants are amphiphilic molecules that have hydrophilic and hydrophobic groups. Any of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants can be used as surfactants. Examples of such surfactants include fatty acids such as lauric acid, oleic acid, sodium laurate, and sodium oleate, or their salts (particularly metal salts). Fatty acids are obtained by hydrolysis of natural fats and oils such as beef tallow, coconut oil, and palm oil. Sodium fatty acids obtained by saponifying fatty acids with sodium hydroxide have long been used as soap. Fatty acids with 8 or more carbon atoms (particularly 10 to 20 carbon atoms) or their salts are considered to be useful as surfactants.

The above surfactants can be used alone or in combination of two or more. For example, according to the manufacturing method described below, when synthesizing a hydrotalcite composition, the surfactant covers the surface of the hydrotalcite compound to form micelles, suppressing the crystal growth of the hydrotalcite compound, and a hydrotalcite composition containing a small-sized hydrotalcite compound can be obtained. In other words, it is easy to adjust the crystallite size of the hydrotalcite compound in the hydrotalcite composition of the present invention. As a result, the surface area can be improved, and the adsorption rate of volatile sulfur compounds (VSCs) can be improved, particularly in the early stage of adsorption.

When the hydrotalcite composition of the present invention contains the above-mentioned surface treatment agent, the content of the hydrotalcite compound is preferably 90.0 to 99.9 mass%, and more preferably 95.0 to 99.8 mass%, based on 100 mass% of the total amount of the hydrotalcite composition of the present invention, from the viewpoints of volatile sulfur compound (VSC) adsorption speed, volatile sulfur compound (VSC) adsorption performance, etc.

The hydrotalcite compound contained in the hydrotalcite composition of the present invention preferably has a crystallite diameter of 1 to 20 nm, more preferably 2 to 15 nm. This makes it easier to obtain a hydrotalcite nanocomposition that is particularly excellent in volatile sulfur compound (VSC) adsorption speed and volatile sulfur compound (VSC) adsorption performance. The crystallite diameter of the hydrotalcite compound contained in the hydrotalcite nanocomposition of the present invention is calculated by a Hall Plot from the half-width at each peak position in the X-ray diffraction diagram.

The hydrotalcite nanocomposition of the present invention preferably has, in the particle size distribution, at least a peak with a maximum particle size of 0.30 to 0.45 μm (particularly 0.35 to 0.40 μm) and a peak with a maximum particle size of 7.50 to 12.00 μm (particularly 8.00 to 11.00 μm). This makes it easier to obtain a hydrotalcite composition that is particularly excellent in terms of volatile sulfur compound (VSC) adsorption speed, volatile sulfur compound (VSC) adsorption performance, etc.

(1-4) Adsorbent for Volatile Sulfur Compounds in a Liquid Phase and Bad Breath Remover The hydrotalcite nanoparticles and hydrotalcite composition of the present invention do not need to be subjected to a high-temperature heat treatment such as 500 ° C. Usually, a hydrotalcite compound becomes an anhydride by heat treatment at a high temperature after reaction, and exerts its adsorption ability. However, the hydrotalcite nanoparticles and hydrotalcite composition of the present invention have the ability to absorb volatile sulfur compounds (VSC) even without heat treatment at a high temperature. For this reason, the hydrotalcite nanoparticles and hydrotalcite composition of the present invention can quickly and sufficiently adsorb volatile sulfur compounds (VSC) by contacting the volatile sulfur compounds in a liquid phase with the hydrotalcite nanoparticles and hydrotalcite composition of the present invention at, for example, 0 to 50 ° C. without heat-treating the reaction product. For this reason, the hydrotalcite nanoparticles and hydrotalcite composition of the present invention are useful as adsorbents for volatile sulfur compounds in a liquid phase (particularly, non-heated adsorbents for volatile sulfur compounds in a liquid phase that are used without heat treatment at high temperatures such as 100°C or higher (particularly 300 to 1000°C)).

The hydrotalcite nanoparticles and hydrotalcite composition of the present invention are also useful as breath fresheners because they can quickly and sufficiently adsorb volatile sulfur compounds (VSCs). In this case, the breath freshener of the present invention may contain toothpaste, oral pharyngeal medicine, etc. Toothpaste can contain abrasives such as calcium hydrogen phosphate, calcium carbonate, and aluminum hydroxide, foaming agents such as sodium lauroyl sarcosyl sulfate, sodium lauryl sulfate, and sucrose fatty acid esters, moisturizers such as sorbitol, glycerin, and propylene glycol, and binders such as alginic acid, as well as the hydrotalcite nanoparticles and hydrotalcite composition of the present invention.

The oral pharyngeal medication also contains ingredients such as cetylpyridinium chloride hydrate, dipotassium glycyrrhizinate, and bellflower extract. The hydrotalcite nanoparticles and hydrotalcite composition of the present invention can be included in the oral pharyngeal medication together with these ingredients.

2. Method for Producing Hydrotalcite Nanoparticles and Hydrotalcite Composition The above-mentioned hydrotalcite nanoparticles and hydrotalcite composition of the present invention are not particularly limited, but can be obtained, for example, by a production method including a step of mixing an aqueous solution containing a zinc salt and an aluminum salt with an aqueous solution containing a surfactant.

The aqueous solution containing zinc salt and aluminum salt is the raw material for the host layer.

Examples of zinc salts include zinc nitrate, zinc sulfate, zinc phosphate, and zinc carbonate. Examples of aluminum salts include aluminum nitrate, aluminum sulfate, and aluminum phosphate. These zinc salts and aluminum salts can be used alone or in combination of two or more. These zinc salts and aluminum salts may also be hydrates.

The concentrations of the zinc salt and aluminum salt in the aqueous solution containing the zinc salt and aluminum salt are not particularly limited, and can be adjusted to the molar ratio of zinc to aluminum in the hydrotalcite compound described above.

The aqueous solution containing zinc salt and aluminum salt may be prepared by adding zinc salt and aluminum salt to water, or by mixing an aqueous solution of zinc salt and an aqueous solution of aluminum salt.

In addition, in the aqueous solution containing a surfactant, the surfactant may be any of those described above. In terms of facilitating the production of the hydrotalcite nanoparticles and hydrotalcite composition of the present invention, the concentration of the surfactant in the aqueous solution containing the surfactant is preferably 0.1 to 2 mol, and more preferably 0.2 to 1.5 mol, per mol of zinc present in the aqueous solution containing the zinc salt and the aluminum salt.

The aqueous solution containing the surfactant may further contain an oxoacid salt such as a carbonate, a nitrate, a sulfate, a borate, or a phosphate. In this case, the aqueous solution containing the surfactant may also be used as a raw material for the guest layer. In this case, the aqueous solution containing the surfactant may be prepared by adding the surfactant and the above-mentioned salt to water, or by mixing an aqueous solution of the surfactant with an aqueous solution of the above-mentioned salt.

Examples of carbonates include sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, lithium carbonate, and ammonium carbonate.

Examples of nitrates include sodium nitrate, potassium nitrate, calcium nitrate, magnesium nitrate, lithium nitrate, and ammonium nitrate.

Examples of sulfates include sodium sulfate, potassium sulfate, calcium sulfate, magnesium sulfate, lithium sulfate, and ammonium sulfate.

Examples of borates include sodium pyroborate, potassium pyroborate, calcium pyroborate, magnesium pyroborate, and lithium pyroborate.

Examples of phosphates include sodium phosphate, potassium phosphate, calcium phosphate, magnesium phosphate, lithium phosphate, ammonium phosphate, etc.

These salts can be used alone or in combination of two or more.

In the aqueous solution containing a surfactant, the concentration of these salts is preferably 1 to 5 mol, and more preferably 2 to 3 mol, per mol of zinc present in the aqueous solution containing the zinc salt and aluminum salt, from the viewpoint of facilitating the production of the hydrotalcite nanoparticles and hydrotalcite composition of the present invention.

In addition, the aqueous solution obtained by mixing an aqueous solution containing a zinc salt and an aluminum salt with an aqueous solution containing a surfactant is preferably an alkaline aqueous solution, since stirring facilitates the co-precipitation of the hydrotalcite nanoparticles and hydrotalcite composition of the present invention. Specifically, after mixing an aqueous solution containing a zinc salt and an aluminum salt with an aqueous solution containing a surfactant, it is preferable to mix a base such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, or lithium carbonate as necessary. These bases can be used alone or in combination of two or more. These bases may also be in the form of an aqueous solution.

The amount of base used is not particularly limited, but it is preferable to appropriately adjust the pH of the aqueous solution containing the zinc salt and aluminum salt and the aqueous solution containing the surfactant to 9 to 12, particularly 9.5 to 11.5, when mixed.

Then, if necessary, the temperature can be raised to a predetermined temperature for hydrothermal synthesis, for example, 20 to 60°C, particularly 30 to 50°C.

Then, the mixture is stirred while maintained at the above-mentioned specified temperature, to obtain the hydrotalcite nanoparticles and hydrotalcite composition of the present invention. The stirring speed and time can be set appropriately, but it is usually preferable to stir at 500 to 1500 rpm for 6 to 48 hours.

If necessary, the solid hydrotalcite nanoparticles and hydrotalcite composition of the present invention can be obtained by centrifuging, suction filtering, drying, etc., according to standard methods. The solid hydrotalcite nanoparticles and hydrotalcite composition of the present invention can then be prepared to a predetermined particle size by classification, crushing, etc. Also, the solid hydrotalcite nanoparticles and hydrotalcite composition can be prepared in various forms, such as a slurry, or granulated by adding a binder, etc.

The present invention will now be described in detail in the form of examples. The following examples are not intended to limit the use of the present invention in any way.

Comparative Example 1: Synthesis of Zn-Al LDH In the general formula (1), Zn-Al LDH was synthesized in which A ^n- is CO ₃ ^2- , n is 2, and x is 0.33. 5.09 g (0.048 mol) of sodium carbonate (Na ₂ CO ₃ , MW 105.9884, volumetric analysis standard, Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed out using an analytical balance (sefi-IBA-200, AS ONE Corporation), and dissolved in 300 mL of ultrapure water (Milli-Q water) collected in a measuring cylinder by stirring at room temperature and 800 rpm for 10 minutes using a stirring bar (4 cm) and a hot stirrer (REXIM RSH-10, AS ONE Corporation) to prepare a 0.16 M sodium carbonate solution. The following reagents were dissolved in the same manner. 3.75 g (0.01 mol) of aluminum nitrate nonahydrate (Al(NO ₃ ) _{3.9H 2} O, MW 375.13, special grade, Fujifilm Wako Pure Chemical Industries, Ltd.) and 5.95 g (0.02 mol) of zinc nitrate hexahydrate (Zn(NO ₃ ) _{2.6H 2} O, MW 297.49, special grade, Kishida Chemical Co., Ltd.) were dissolved in 100 mL of Milli-Q water to prepare a mixed nitrate solution (0.1 M Al(NO ₃ ) _{3.9H 2} O, 0.2 M Zn(NO ₃ ) _{2.6H 2} O). In addition, 4.00 g of sodium hydroxide (NaOH, MW 39.997, special grade, Kishida Chemical Co., Ltd.) was dissolved in 100 mL of Milli-Q water to prepare a 2 M sodium hydroxide solution. While stirring the sodium carbonate aqueous solution in the same manner using a stirrer and a hot stirrer, the nitrate mixed aqueous solution was dropped in a burette at a rate of 10±0.5mL/min. An aqueous sodium hydroxide solution was appropriately added so that the pH during the drop of the nitrate mixed aqueous solution was 10.5±0.2. After the end of the drop of the nitrate mixed aqueous solution, the mixture was stirred at 40°C and 1000 rpm for 24 hours, and the precipitate was separated into solid and liquid by suction filtration using a Kiriyama funnel, a suction bell, and an aspirator (A-3S, EYELA Tokyo Rikakikai Co., Ltd.) and filter paper (5C), and washed three times with 200mL of Milli-Q water. The obtained product was dried at 80°C for 18 hours in a program constant temperature dryer (DOV-450P, AS ONE Co., Ltd.), and then crushed in an agate mortar to obtain product A. The pH was measured using a pH meter (D-51, Horiba, Ltd.), and Milli-Q water was collected from an ultrapure water production system (Direct-Q, Merck Ltd.) and used in the experiments.

Example 1: Synthesis of Zn-Al LDH using sodium laurate Zn-Al LDH was synthesized in which A ^n- is CO ₃ ^2- , n is 2, and x is 0.33 in the general formula (1). 5.09 g (0.048 mol) of sodium carbonate (Na ₂ CO ₃ , MW 105.9884, volumetric analysis standard, Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed out using an analytical balance (sefi-IBA-200, AS ONE Corporation), and dissolved in 300 mL of ultrapure water (Milli-Q water) collected in a measuring cylinder by stirring at room temperature and 800 rpm for 10 minutes using a stirring bar (4 cm) and a hot stirrer (REXIM RSH-10, AS ONE Corporation) to prepare a 0.16 M sodium carbonate solution. The following reagents were dissolved in the same manner. 3.75 g (0.01 mol) of aluminum nitrate nonahydrate (Al(NO ₃ ) _{3.9H 2} O, MW 375.13, special grade, Fujifilm Wako Pure Chemical Industries, Ltd.) and 5.95 g (0.02 mol) of zinc nitrate hexahydrate (Zn(NO ₃ ) _{2.6H 2} O, MW 297.49, special grade, Kishida Chemical Co., Ltd.) were dissolved in 100 mL of Milli-Q water to prepare a mixed nitrate solution (0.1 M Al(NO ₃ ) _{3.9H 2} O, 0.2 M Zn(NO ₃ ) _{2.6H 2} O). In addition, 4.00 g of sodium hydroxide (NaOH, MW 39.997, special grade, Kishida Chemical Co., Ltd.) was dissolved in 100 mL of Milli-Q water to prepare a 2 M sodium hydroxide solution. Further, 0.444 g (0.002 mol) of sodium laurate (CH ₃ (CH ₂ ) ₁₀ COONa, MW 222.30, Grade 1, Kishida Chemical Co., Ltd.) precisely weighed on an analytical balance was added to 50 mL of Milli-Q water, and the temperature of a hot stirrer was set to 60° C. and stirred at 400 rpm for 1 hour to obtain an aqueous sodium laurate solution. After adding the aqueous sodium laurate solution to the aqueous sodium carbonate solution, the solution was stirred at room temperature at 800 rpm using a stirrer and a hot stirrer, and the aqueous nitrate solution was added dropwise with a burette at a rate of 10±0.5 mL/min. An aqueous sodium hydroxide solution was appropriately added so that the pH of the aqueous nitrate solution during the dropwise addition became 10.5±0.2. After the dropwise addition of the nitrate mixed aqueous solution was completed, the mixture was stirred at 40°C and 1000 rpm for 24 hours, then centrifuged at 4000 rpm for 3 min in a tabletop centrifuge (2410, Kubota Shoji Co., Ltd.), water was removed by decantation, and then Milli-Q water was added, stirred, and centrifuged five times for washing. Thereafter, the precipitate was separated into solid and liquid by suction filtration using a Kiriyama funnel, a suction bell, and an aspirator (A-3S, EYELA Tokyo Rikakikai Co., Ltd.) and filter paper (5C). The obtained product was dried at 80°C for 18 hours in a program constant temperature dryer (DOV-450P, AS ONE Co., Ltd.), and then crushed in an agate mortar to obtain product B. The pH was measured using a pH meter (D-51, Horiba, Ltd.), and Milli-Q water was collected from an ultrapure water production system (Direct-Q, Merck Ltd.) and used in the experiments.

Example 2: Synthesis of Zn-Al LDH using oleic acid Zn-Al LDH was synthesized in which A ^n- is CO ₃ ^2- , n is 2, and x is 0.33 in the general formula (1). 5.09 g (0.048 mol) of sodium carbonate (Na ₂ CO ₃ , MW 105.9884, volumetric analysis standard, Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed out using an analytical balance (sefi-IBA-200, AS ONE Corporation), and dissolved in 300 mL of ultrapure water (Milli-Q water) collected in a measuring cylinder by stirring at room temperature and 800 rpm for 10 minutes using a stirring bar (4 cm) and a hot stirrer (REXIM RSH-10, AS ONE Corporation) to prepare a 0.16 M sodium carbonate solution. The following reagents were dissolved in the same manner. 3.75 g (0.01 mol) of aluminum nitrate nonahydrate (Al(NO ₃ ) _{3.9H 2} O, MW 375.13, special grade, Fujifilm Wako Pure Chemical Industries, Ltd.) and 5.95 g (0.02 mol) of zinc nitrate hexahydrate (Zn(NO ₃ ) _{2.6H 2} O, MW 297.49, special grade, Kishida Chemical Co., Ltd.) were dissolved in 100 mL of Milli-Q water to prepare a mixed nitrate solution (0.1 M Al(NO ₃ ) _{3.9H 2} O, 0.2 M Zn(NO ₃ ) _{2.6H 2} O). In addition, 4.00 g of sodium hydroxide (NaOH, MW 39.997, special grade, Kishida Chemical Co., Ltd.) was dissolved in 100 mL of Milli-Q water to prepare a 2 M sodium hydroxide solution. Further, 0.56 g (0.002 mol) of oleic acid (CH ₃ (CH ₂ ) ₇ CH═CH(CH ₂ ) ₇ COOH, MW 282.47, Grade 1, Kishida Chemical Co., Ltd.) precisely weighed on an analytical balance was added to 50 mL of Milli-Q water, and the temperature of a hot stirrer was set to 70° C. and stirred at 800 rpm for 1 hour to obtain an aqueous solution of oleic acid. After adding the aqueous solution of oleic acid to the aqueous solution of sodium carbonate, the aqueous solution of nitrates was added dropwise with a burette at a rate of 10±0.5 mL/min while stirring at room temperature at 800 rpm using a stirrer and a hot stirrer. An aqueous solution of sodium hydroxide was appropriately added so that the pH of the aqueous solution of nitrates was 10.5±0.2 during the dropping. After the dropwise addition of the nitrate mixed aqueous solution was completed, the mixture was stirred at 40°C and 1000 rpm for 24 hours, then centrifuged at 4000 rpm for 3 min in a tabletop centrifuge (2410, Kubota Shoji Co., Ltd.), water was removed by decantation, and then Milli-Q water was added, stirred, and centrifuged five times for washing. Thereafter, the precipitate was separated into solid and liquid by suction filtration using a Kiriyama funnel, a suction bell, and an aspirator (A-3S, EYELA Tokyo Rikakikai Co., Ltd.) and filter paper (5C). The obtained product was dried at 80°C for 18 hours in a program constant temperature dryer (DOV-450P, AS ONE Co., Ltd.), and then crushed in an agate mortar to obtain product C. The pH was measured using a pH meter (D-51, Horiba, Ltd.), and Milli-Q water was collected from an ultrapure water production system (Direct-Q, Merck Ltd.) and used in the experiments.

Reference Example 1: Synthesis of ZnO by Precipitation Method The synthesis of ZnO by precipitation method was carried out by the following procedure. A Liebig cooler and a thermometer with a silicone stopper were connected to a four-necked separable flask. 70 mL of Milli-Q water collected in a measuring cylinder and 9.54 g (1.00 mol) of zinc chloride (ZnCl ₂ , MW 136.315, first grade, Fujifilm Wako Pure Chemical Industries, Ltd.) weighed on an analytical balance were added to the four-necked separable flask, and the mixture was stirred at room temperature and 800 rpm using a stirrer (4 cm) and a hot stirrer (REXIM RSH-10, AS ONE Co., Ltd.). In addition, using another hot stirrer, 10 mL of 28% ammonia water (NH ₃ , MW 17.03, special grade, Kishida Chemical Co., Ltd.) was added to a conical flask with a silicone stopper connected to a tube, and heated to 80°C. Vaporized ammonia was introduced into the zinc chloride aqueous solution through a tube. During the introduction of ammonia gas, the pH of the solution was measured, and the introduction of ammonia gas was stopped when the pH reached 7.5. Thereafter, the mixture was stirred at 90°C and 800 rpm for 6 hours, and the precipitate was separated into solid and liquid by suction filtration using a Kiriyama funnel, a suction bell, and an aspirator (A-3S, EYELA Tokyo Rikakikai Co., Ltd.) and filter paper (5C), and washed three times with 200 mL of Milli-Q water. The obtained product was dried in a constant temperature dryer at 80°C for 18 hours, and then crushed in an agate mortar to obtain product D.

Reference Example 2: Synthesis of ZnO by mechanochemical method ZnO was synthesized by the mechanochemical method according to the following procedure (Scripta Mater., 44(8-9), 1731-1734(2001)). 2.73 g (0.02 mol) of zinc chloride (ZnCl ₂ , MW 136.315, first grade, Fujifilm Wako Pure Chemical Industries, Ltd.), 2.12 g (0.02 mol) of sodium carbonate (Na ₂ CO ₃ , MW 105.99, special grade, Fujifilm Wako Pure Chemical Industries, Ltd.), and 10.05 g (0.172 mol) of sodium chloride (NaCl, MW 58.44, special grade, Kishida Chemical Industries, Ltd.) were weighed out on an analytical balance and dried for 2 h at 150° C. in a constant temperature dryer before use. Then, together with 150 g of zirconia balls (YTZ-10, diameter 10 mm, AS ONE Co., Ltd.), it was placed in a pot mill (HD-A-4, AS ONE Co., Ltd.) and pulverized at room temperature and 110 rpm for 3 h on a tabletop pot mill rotating table (BALL MILL ANZ-51S, Nitto Kagaku Co., Ltd.). It was placed in an alumina crucible (PSA-100S, Tokyo Glass Instruments Co., Ltd.) and heat-treated in air at 400 ° C. for 0.5 h in a Fine tabletop electric furnace (F-1404-P, Tokyo Glass Instruments Co., Ltd.). The temperature was increased and decreased at 12 ° C./min. After the heat treatment, the product was placed in a centrifuge tube together with Milli-Q water and washed five times at 4000 rpm for 3 min in a tabletop centrifuge. It was then dried at 60 ° C. for 10 h in a constant temperature dryer. After drying, the mixture was crushed using an agate mortar to obtain Product E.

Reference Example 3: Synthesis of ZnO by hydrothermal synthesis ZnO was synthesized by hydrothermal synthesis according to the following procedure (Solid State Communications, 113(6), 363-366 (2000)). 50 mL of Milli-Q water weighed with a measuring cylinder and 2.04 g (0.015 mol) of zinc chloride (ZnCl ₂ , MW 136.315, first grade, Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a 200 mL beaker to prepare a 0.3 M zinc chloride solution. In addition, 1.2 g (0.03 mol) of sodium hydroxide (NaOH, MW 39.997, special grade, Kishida Chemical Co., Ltd.) was added to 50 mL of Milli-Q water to prepare a 0.6 M aqueous sodium hydroxide solution. Next, 50 mL of Milli-Q water was added to 5 mL of hydrochloric acid (MW 36.46, containing 35% hydrogen chloride, special grade, Kishida Chemical Co., Ltd.) to adjust the pH. When preparing each solution, the reagent was dissolved by stirring using a stir bar and a hot stirrer (As One Corporation, REXIM RSH-1DN). Milli-Q water was collected from an ultrapure water production system (Direct-Q, Merck Co., Ltd.) and weighed into a 100 mL measuring cylinder. An analytical balance was used to weigh the reagents.

0.3M zinc chloride solution was stirred at 600 rpm with a hot stirrer while 0.6M aqueous sodium hydroxide solution was added to obtain a zinc hydroxide precipitate. The precipitate was suction filtered using a Kiriyama funnel (KIRIYAMA, SU-60), a suction bell (KIRIYAMA, VKU-500, AS ONE Co., Ltd.), an aspirator (A-3S, EYELA Tokyo Rikakikai Co., Ltd.), and filter paper (AS ONE Co., Ltd., φ60 mm, No. 5C). The precipitate thus obtained was dispersed in 100 mL of Milli-Q water. Then, hydrochloric acid was added to adjust the pH to 6.5, and the mixture was stirred at 600 rpm and room temperature for 3 hours. After stirring, the solution was placed in a Teflon (registered trademark) container, sealed, and heated at 100°C for 10 hours in a constant temperature dryer (ETTAS, EOP-450V). It was then suction filtered and dried at room temperature. After drying, the product was crushed in an agate mortar to obtain product F as a white powder.

Test Example 1: Identification of crystalline phase by XRD The crystalline phase of the obtained product was identified by powder X-ray diffraction (XRD). Measurement was performed using an X-ray diffractometer (RINT2200, Rigaku Co., Ltd.), a target of Co, a monochromator, and analysis software (JADE6, Rigaku Co., Ltd.) to identify the crystalline phase. The measurement conditions for products A, B, and C were a scan range of 10 to 80°, a sampling width of 0.02°, a scan speed of 2.0°/min, an applied voltage of 40 kV, an applied current of 20 mA, an emission slit of 1°, a scattering slit of 1°, and a receiving slit of 0.3 mm. On the other hand, the measurement conditions for products D, E, and F were a scan range of 10 to 70°, a sampling width of 0.02°, a scan speed of 2.0°/min, an applied voltage of 40 kV, an applied current of 20 mA, an emission slit of 1°, a scattering slit of 1°, and a receiving slit of 0.3 mm. The sample was finely ground in an agate mortar, and filled into a 20 x ¹⁸ mm2 glass sample holder (Rigaku Corp.) with a 0.5 mm deep indentation, and then attached to an X-ray diffractometer so that the diffraction plane was revealed. In the measurement, peak correction was performed using the internal standard method. 0.10 g of sample was mixed with 0.05 g of metallic silicon (99.99%, Mitsuwa Chemical Co., Ltd.), ground, and subjected to the measurement.

The powder X-ray diffraction patterns of product A of Comparative Example 1, product B of Example 1, and product C of Example 2 are shown in Figure 1. The peaks of products A, B, and C matched the diffraction peaks of zinc aluminum carbonate hydroxide hydrate (Zn-Al LDH) from the ICDD data.

The powder X-ray diffraction patterns of product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3 are shown in Figure 2. The peaks of products D, E, and F matched the diffraction peaks of zincite in the ICDD data.

Test Example 2: Identification of crystallite size by Hall Plot The crystallite size of each sample was calculated and identified from the half-width at each peak position in the X-ray diffraction pattern. The width and intensity of the peak in the X-ray diffraction pattern depend on the crystallite size and lattice distortion of the powder sample being measured. Therefore, the half-width β _hkl at each diffraction plane calculated by the integrated intensity calculation of XRD is composed of the half-width β _D derived from the crystallite size and the half-width β _S derived from the lattice distortion, and is expressed by the following formula.

Regarding the half-width _βD derived from the crystallite diameter and the half-width _βS derived from the lattice distortion, D is the crystallite diameter [Å], θ is the Bragg angle [rad] of the measurement plane, K is the Scherrer constant (=0.94), and λ is the wavelength of the measurement X-ray ((Co)=1.792 [Å]),

Then, the half width β _hkl can be transformed as follows:

In other words, the crystallite size can be determined from the intercept, and the lattice distortion can be determined from the inclination.

The range from when the peak intensity starts to appear until it drops off at each peak position of the sample measured in XRD is measured at a scan speed of 0.10°/min, the integrated intensity is calculated for that range, and the half-width _βhkl at each peak position (diffraction plane) is calculated. Then, a graph is drawn with 4 sin θ on the horizontal axis and _βhkl cos θ on the vertical axis. If the intercept of the approximation line of the drawn graph is b, then

The crystallite size can be calculated using this formula (Solid State Sci., 13(1), 251-256 (2011)).

The crystallite size was calculated using the integrated intensity including the background. If the peak is too small, it may be confused with the background in the calculation of the integrated intensity of XRD. Therefore, in the case of Zn-Al LDH (products A, B, and C), of the 15 peaks appearing in the range of 2θ = 10 to 80°, 7 peaks with peak intensities of 8 or more (maximum peak intensity is 100) recorded in the ICDD data were used. On the other hand, in the case of ZnO (products D, E, and F), all 5 peaks appearing in the range of 2θ = 10 to 70° were used. The average value was calculated instead of the crystallite size for each crystal orientation.

The peak position 2θ, crystal plane (hkl), half width β _hkl , 4 sin θ, and β _hkl cos θ values used in the Hall Plot are shown in Table 1 for product A of Comparative Example 1, product B of Example 1, and product C of Example 2. In addition, the points and approximate straight lines with 4 sin θ on the horizontal axis and β _hkl cos θ on the vertical axis for product A of Comparative Example 1, product B of Example 1, and product C of Example 2 are shown in FIG. 3. In addition, the intercept value of the approximate straight line was substituted into the formula (2.2) to obtain the crystallite size. The crystallite sizes of product A of Comparative Example 1, product B of Example 1, and product C of Example 2 were 25.9 nm, 13.8 nm, and 12.5 nm, respectively.

Similarly, the values of the peak position 2θ, crystal plane (hkl), half-width β _hkl , 4 sin θ, and β _hkl cos θ used in the Hall Plot are shown in Table 2 for product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3. In addition, the points and the approximate line with the horizontal axis being 4 sin θ and the vertical axis being β _hkl cos θ for product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3 are shown in FIG. 4. In addition, the intercept value of the approximate line was substituted into the formula (2.2) to obtain the crystallite size. The crystallite sizes of product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3 were 48.2 nm, 31.2 nm, and 24.1 nm, respectively.

Test Example 3: SEM image observation and elemental analysis by EDS Each product was fixed to an aluminum plate of 10 mm x 10 mm with conductive tape (7321, Nisshin EM Co., Ltd.) and dried at room temperature for 24 hours using a vacuum dryer (KVO-300, AS ONE Co., Ltd.). Using an Osmium Plasma Coater (OPC60A, Filgen Co., Ltd.), osmium oxide (OSO4) was coated to a thickness of 12 nm. The field emission scanning electron microscope used was FE-SEM (JSM6500FS, JEOL Co., Ltd.). In addition, elemental analysis was performed on Product A of Comparative Example 1, Product B of Example 1, and Product C of Example 2 to determine the ratio of Zn to Al. The elemental analysis was performed using EDS (JSM-6460LA, JEOL Co., Ltd.). Simplified quantitative analysis (ZAF method) was performed at an acceleration voltage of 25 kV, a degree of vacuum of 5.00×10 ⁻⁴ Pa or less, an irradiation current of 10 A, and an irradiation time of 200 s.

SEM images and EDS profiles of product A of Comparative Example 1, product B of Example 1, and product C of Example 2 are shown in Figures 5 to 7, and the ratio of the number of Zn and Al atoms is shown in Table 3.

The SEM image of product A in Comparative Example 1 shows the appearance of an aggregation of particles of about 1 μm. The atomic ratio of Zn to Al was 2.01, and it can be seen that there was little variation depending on the measurement location, and a hydrotalcite compound of the prescribed composition [Zn ²⁺ _1−x Al ³⁺ _x (OH) ₂ ][(CO ₃ ²⁻ ) _x/2 ·mH ₂ O] (x = 0.33) was obtained.

The SEM image of product B in Example 1 shows that particles aggregated to form a layer. The atomic ratio of Zn to Al was 2.19, and there was more Zn than the amount charged. It is believed that some zinc compounds were formed, and the composition was [Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ·mH ₂ O] (x = 0.31).

The SEM image of product C in Example 2 shows that particles of about 1 μm are aggregated. The atomic ratio of Zn to Al is 2.32, and there is more Zn than the charged amount. It is believed that some zinc compounds were generated, and the composition was [Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ·mH ₂ O] (x = 0.30).

Figure 8 shows SEM images of product D of Reference Example 1, product E of Reference Example 2, and product F of Reference Example 3. Product D appears to be an agglomeration of plate-like particles of about 3 to 10 μm, while products E and F appear to be an agglomeration of particles less than 1 μm.

Test Example 4: FT-IR Spectroscopic Analysis Measurement was performed using a Fourier transform infrared spectrometer (FT/IR-430, JASCO Corporation) with a measurement range of 400 to 1400 cm ⁻¹ , an accumulation count of 100, and a resolution of 4 cm ⁻¹ . Spectral analysis was performed using analysis software (Spectra Manager, JASCO Corporation). The measurement sample was prepared by the KBr agent method. The sample was added to KBr (special grade, FUJIFILM Wako Pure Chemical Industries, Ltd.) fine powder at a ratio of 0.1% by mass, pulverized in an agate mortar, mixed well, and then placed in a tablet molder and pressed with a hydraulic molder (MP-1, JASCO Corporation).

FIG. 9 shows FT-IR spectra of Product A of Comparative Example 1, Product B of Example 1, and Product C of Example 2. The absorption peak seen around 3400 cm ^-1 is due to the stretching and bending vibrations of hydrogen bonds of hydroxyl groups, the absorption peaks seen from 2850 to 2950 cm ^-1 are due to hydrogen bonds between interlayer water and anions, the absorption peaks seen at 1360 cm ^-1 , 1940 cm ^-1 , and 790 cm ^-1 are due to carbonate ions, the absorption peaks seen at 618 cm ^-1 and 428 cm ^-1 are due to the vibrations of Al-OH bonds and Zn-OH bonds, respectively, and the absorption peak seen at 552 cm ^-1 is due to the vibration of Al-O bonds (Revista Brasilera de Ciencia do Solo, 39(1), pp.1-13 (2015), Univ. for Science, 11(1), pp.90-100 (2015), J. Nanoparticles, vol. Res., 2(3), 293-298(2000), J. Alloys and Compounds, 539(1), 154-160(2012)).

In addition to the above, Product B in Example 1 also showed absorption peaks at 2924 cm ⁻¹ and 2854 cm ⁻¹ . This was due to the stretching vibration of CH ₂ derived from sodium laurate (Univ. for Science, 11(1), pp.90-100 (2015)).

Similarly, in the case of Product C of Example 2, absorption peaks were observed at 2924 cm ⁻¹ and 2854 cm ⁻¹ , which were due to the stretching vibration of CH ₂ derived from oleic acid (Chem. Eng. J., 119 (2-3), 71-81 (2006)).

Figure 10 shows the FT-IR spectra of product D from Reference Example 1, product E from Reference Example 2, and product F from Reference Example 3.

Regarding the product D of Reference Example 1, the absorption peak observed near 3,400 cm ⁻¹ is due to the stretching and bending vibrations of the hydrogen bond of the hydroxyl group, the absorption peak observed at 428 cm ⁻¹ is due to the vibration of the Zn—OH bond, and the absorption peak observed at 457 cm ⁻¹ is due to the vibration of the Zn—O bond (J. Advanced Ceramics, 2(3), 260-265 (2013), Revista Brasilera de Ciencia do Solo, 39(1), pp.1-13 (2015), J. Alloys and Compounds, 539(1), 154-160 (2012)).

In the case of Product E of Reference Example 2 and Product F of Reference Example 3, no absorption peak was observed at 428 cm ^-1 , and the presence of a hydroxyl group was not confirmed.

Test Example 5: Particle Size Distribution Measurement The particle size distribution of each product was measured using a laser diffraction/scattering type measuring device (LA920, Horiba, Ltd.). Ultrapure water (product A, product D, product E, and product F) or isopropyl alcohol (product B and product C) was used as the dispersion medium. In order to prevent particle aggregation, the particles were dispersed by applying ultrasonic vibrations (15 minutes for product A, product B, and product C, and 5 minutes for product D, product E, and product F) with an ultrasonic probe in the device, and then the measurement was performed. The relative refractive index to the dispersion medium was 1.10 for product A, 1.05 for product B and product C, and 1.50 for product D, product E, and product F. The lower limit of the measurement range of the laser diffraction/scattering type measuring device (LA920, Horiba, Ltd.) is 200 nm, and the particle size of powder (secondary particles), which is an aggregate of primary particles, can be measured.

The particle size distribution measurement results for Product A of Comparative Example 1, Product B of Example 1, and Product C of Example 2 are shown in Figure 11 and Table 4.

The particle size distribution of product A in Comparative Example 1 has two peaks at particle sizes of 0.51 μm and 6.72 μm, which account for approximately 20% and 80% of the area. This suggests that the product is an aggregate consisting of primary particles (crystallites) of 25.9 nm.

The particle size distribution of product B in Example 1 had two peaks at particle sizes of 0.39 μm and 8.82 μm, accounting for approximately 60% and 40%, respectively. This suggests that there was a higher frequency of particles with smaller particle sizes compared to product A, and that these particles were dispersed by lauric acid.

The particle size distribution of product C in Example 2 has three peaks at particle sizes of 0.39 μm, 10.10 μm, and 77.34 μm. The frequency of 0.39 μm is high, but there is also a peak at 77.34, and it appears that the dispersing effect of oleic acid is slightly lower than that of lauric acid.

The particle size distribution measurement results for Product D of Reference Example 1, Product E of Reference Example 2, and Product F of Reference Example 3 are shown in Figure 12 and Table 5.

The particle size distribution peaks are seen at two locations, at particle sizes of 0.45 μm and 5.87 μm, for Product D of Reference Example 1, two locations, at particle sizes of 3.41 μm and 5.12 μm, for Product E of Reference Example 2, and one location, at 5.12 μm, for Product F of Reference Example 3. Product E of Reference Example 2 and Product F of Reference Example 3 are more cohesive than Product D of Reference Example 1, but the particle size distribution shows a relatively uniform profile, suggesting that relatively uniform aggregates were obtained.

Test Example 6: Adsorption experiment of hydrogen sulfide (6-1) Preparation of hydrogen sulfide water A silicon stopper and a silicon stopper with a glass tube were attached to two side tubes of a 500 mL four-neck flask. In addition, 150 mL of Milli-Q water was placed in a 200 mL Erlenmeyer flask, and a glass tube and a bubbling tube were attached through the silicon stopper. The glass tube of the four-neck flask and the bubbling tube of the Erlenmeyer flask were connected via a silicon tube and a two-way cock. In addition, a gas washing bottle filled with 1 mol/L sodium hydroxide aqueous solution was connected to the glass tube of the Erlenmeyer flask via a silicon tube. A calcium chloride tube was attached to the gas washing bottle via a silicon tube.

3 g of iron sulfide (first-grade, Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed out using an analytical balance and placed in a four-neck flask. 15 mL of 1 mol/L dilute sulfuric acid was added from a separating funnel to generate hydrogen sulfide. The generated hydrogen sulfide was passed through Milli-Q water in an Erlenmeyer flask and bubbled for approximately 15 minutes. The 1 mol/L dilute sulfuric acid was prepared by weighing sulfuric acid (special grade, Fujifilm Wako Pure Chemical Industries, Ltd.) into a measuring cylinder and diluting it 36 times. These operations were performed in a draft chamber while wearing rubber gloves, protective glasses, and a gas mask.

(6-2) Adsorption and collection device A screw-equipped side tube was attached to a commercially available 200 mL Erlenmeyer flask. A hole cap with a septum was attached to the side tube, and a separatory funnel was attached to the other side via a silicone plug, and a stirrer was placed in it. 10 mL and 15 mL of the hydrogen sulfide water prepared in (6-1) were weighed out with a volumetric pipette, and Milli-Q water was added to dilute them 15 times and 10 times, respectively, to prepare two types of hydrogen sulfide water (H ₂ S water) with a total volume of 150 mL. Immediately after preparation, the H ₂ S water tries to reach equilibrium between the gas phase and the liquid phase, so the hydrogen sulfide concentration changes in both the gas phase and the liquid phase. Therefore, in order to quickly transition to equilibrium, the solution was stirred at room temperature at 300 rpm for 60 minutes using a hot stirrer.

(6-3) Adsorption experiment 0.10 g of the product was weighed on an analytical balance and dropped from an analytical funnel into H ₂ S water in a two-neck flask. Before weighing, it was dried at 80° C. for 18 hours in a constant temperature dryer (DO-300PC, AS ONE Co., Ltd.). The H ₂ S water was stirred, and gas or H ₂ S aqueous solution was collected from the gas phase (head space) in the flask or the H ₂ S aqueous solution after 0 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or 18 hours with a syringe. 30 μL of gas was collected using a gas-tight syringe (MS-GAN025, Ito Seisakusho Co., Ltd.), and 2 μL of H ₂ S water was collected using a microsyringe (701N standard type PT-2 10 μL, Hamilton Co., Ltd.). The concentrations of the collected gas and H ₂ S water were measured with a gas chromatograph equipped with a flame photometric detector. The H ₂ S water was collected using the solvent flush injection method, which involves sequentially introducing into a syringe 1 μL of predetermined amounts of Milli-Q water, air, 2 μL of the measurement solution (H ₂ S water), and air, thereby avoiding residual sample in the needle and reducing measurement errors.

The change in total sulfide concentration in the H ₂ S water and headspace in the sealed container after products A to D were added is shown in Table 6 when a 15-fold diluted H ₂ S aqueous solution was used, and in Table 7 when a 10-fold diluted H ₂ S aqueous solution was used. As a blank, the case without a sample is also shown.

The total sulfide concentration in the sealed container before addition was taken as 100%, and the rate of change over time in the sulfide concentration after adding products A, B, and C is shown in Figure 13 for a 15-fold diluted _H2S aqueous solution (upper figure) and a 10-fold diluted _H2S aqueous solution (lower figure).

The change over time in the sulfide concentration in the H ₂ S water and head space in the closed container is shown in FIG. 14 for the 15-fold diluted H ₂ S aqueous solution, and in FIG. 15 for the 10-fold diluted H ₂ S aqueous solution.

In the absence of a sample, the sulfide concentrations in both the headspace and H ₂ S water increased or decreased slightly in both the 15-fold and 10-fold diluted H ₂ S aqueous solutions, but hardly any change was observed.

As shown in Figures 14 and 15, for products A, B, and C, the sulfide concentration in the headspace quickly decreased to 0. For product D, it reached 0 slightly later than the others. On the other hand, for products A, B, C, and D, once the sulfide concentration in the _H2S water decreased to a certain concentration, it hardly increased or decreased thereafter, reaching the adsorption equilibrium, and the concentration did not become 0. It took longer to reach the adsorption equilibrium when 10-fold diluted _H2S water was used than when 15-fold diluted _H2S water was used. From this, it is presumed that the total amount of sulfide that can be adsorbed for each product is even greater.

As shown in FIG. 13, in the case of 15-fold diluted H ₂ S water, the sulfide concentration of product A decreased to 34.5% in 1 hour and to 14.4% in 18 hours after the addition. The sulfide concentration of product B decreased to 27.8% in 1 hour and to 12.8% in 18 hours, and the sulfide concentration of product C decreased to 28.2% in 1 hour and to 14.4% in 18 hours. As shown in FIG. 13, in the case of 10-fold diluted H ₂ S water, the sulfide concentration of product A decreased to 57.9% in 1 hour and to 22.2% in 18 hours after the addition. The sulfide concentration of product B decreased to 45.3% in 1 hour and to 16.3% in 18 hours, and the sulfide concentration of product C decreased to 44.6% in 1 hour and to 20.8% in 18 hours. In particular, the sulfide concentrations of products B and C decreased significantly one hour after the addition. For example, when 10-fold diluted _H2S water was used, it was understood that after 1 hour, products B and C had a higher adsorption rate by about 13% than product A. The difference in adsorption rate is considered to be due to the fact that products B and C have small primary particle sizes, the powder as aggregates is also dispersed, and the contact area is large.

Regarding products D, E and F, in the case of 15-fold diluted _H2S water, the sulfide concentration of product D decreased to 62.6% in 1 hour after the addition, and to 32.2% in 18 hours. In the case of 10-fold diluted _H2S water, the sulfide concentration of product D decreased to 61.8% in 1 hour after the addition, and to 31.6% in 18 hours. The sulfide concentration of product E decreased to 36.7% in 1 hour, and to 23.6% in 18 hours, while the sulfide concentration of product F decreased to 33.8% in 1 hour, and to 20.2% in 18 hours. Compared to product D, products E and F decreased more quickly, with a difference of about 40% in 15-fold diluted _H2S water and about 25% in 10-fold diluted _H2S water after 1 hour. From these facts and the measurement results of the crystallite size in Test Example 2 and the particle size distribution in Test Example 5, it is believed that although Product D contains smaller particles, it also contains a considerable amount of large particles, and that Products E and F, which have smaller and more uniform particle sizes, are more advantageous for adsorption.

18 hours after the product was added, the sulfide adsorption amount was Product D < Product A ≒ Product E ≒ Product F < Product C < Product B. The amount of Zn contained in 0.1 g of product was 0.038 g for Zn-Al LDH (Product A, Product B, and Product C), and 0.080 g for ZnO (Product E and Product F), which is high, but Product A, Product E, and Product F show the same adsorption amount. The sulfide adsorption amount is thought to depend not on the amount of Zn contained, but on the amount of Zn exposed on the contact surface. Product A has a layered structure, and due to contact with the Zn exposed between the layers, it shows the same adsorption amount as Product E and Product F, which contain more Zn. In other words, it can be understood that Product B and Product C have even better adsorption performance.

Regarding the adsorption rate, when product A and product F, which have the same crystallite size and median diameter, are compared, the sulfide concentration after 1 hour is lower in product F, but after 18 hours, the concentrations are about the same. ZnO is surface adsorbed, but after surface adsorption of Zn-Al LDH, it is believed that sulfide migrates to the interlayer, where anion exchange and exchange between interlayer water and free _H2S proceed.

Test Example 7: Analysis of Samples after Adsorption Test (7-1) XRD
X-ray diffraction patterns of products A, B and C before and after the adsorption experiment in Test Example 6 are shown in Figure 16. Metallic silicon was used as the internal standard. In all cases, almost no shift in peak position was observed before and after the adsorption experiment. This is thought to be due to the replacement of carbonate ions _CO3 ^2- and water, which are anions between the layers of LDH, with hydrogen sulfide ions ^HS- and free _H2S , and although one _CO3 ^2- is replaced with two ^HS- due to charge balance, this is thought to be because the difference in occupied size is small.

Figure 17 shows the X-ray diffraction patterns of products D, E, and F before and after the adsorption experiment. Metallic silicon was used as the internal standard. No peak shifts or unknown peaks were observed before and after sulfide adsorption, and no peaks corresponding to ZnS were found. It is believed that sulfide was adsorbed on the particle surface or between particles.

(7-2) SEM Image Observation and EDS Elemental Analysis SEM images and EDS profiles of products A, B, and C after the sulfide adsorption experiment are shown in FIGS.

In all cases, trace amounts of S were detected in the EDS profiles. The Zn to Al ratios were 2.46, 2.39 and 2.30 for product A, product B and product C, respectively, and the compositions were [Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ·mH ₂ O] (x = 0.29), [Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ·mH ₂ O] (x = 0.29), [Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(CO ₃ ^2- ) _x/2 ·mH ₂ O] (x = 0.30), respectively.

Figures 21 to 23 show SEM images and EDS profiles of products D, E, and F after sulfide adsorption experiments. No S was detected in the EDS profiles in any of the cases.

SEM/EDS analysis is performed under high vacuum, and the sample surface is irradiated with an electron beam, so sulfides attached to the surface are quickly desorbed. On the other hand, sulfides that were ion- and molecular-exchanged between the layers of Zn-Al LDH are thought to have been detected without being desorbed, and a clear difference appears to have arisen between products A, B, and C and products D, E, and F. In other words, it can be seen that hydrogen sulfide is more strongly adsorbed in products A, B, and C than in products D, E, and F.

Claims (12)

A volatile sulfur compound adsorbent in a liquid phase, which contains a hydrotalcite compound containing divalent zinc ions and trivalent aluminum ions, and which contains hydrotalcite nanoparticles having a crystallite size of 1 to 20 nm. The hydrotalcite compound is represented by the general formula (1):
[Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ ][(A ^n- ) _x/n ·mH ₂ O] (1) [wherein, 0<x<1. ^{A n-} represents an anion. n represents 1 or 2. m represents an integer of 1 or more.]
The adsorbent for volatile sulfur compounds in a liquid phase according to claim 1, having a composition represented by the formula: The adsorbent for volatile sulfur compounds in a liquid phase according to claim 2, wherein x is 0.2 to 0.6. The adsorbent for volatile sulfur compounds in a liquid phase according to any one of claims 1 to 3, wherein the hydrotalcite nanoparticles have at least a peak in the particle size distribution where the maximum particle diameter is 0.30 to 0.45 μm and a peak where the maximum particle diameter is 7.50 to 12.00 μm. A breath odor remover comprising the liquid phase volatile sulfur compound adsorbent according to any one of claims 1 to 4 . A method for producing an adsorbent for volatile sulfur compounds in a liquid phase according to any one of claims 1 to 4 , comprising the steps of:
A manufacturing method comprising a step of mixing an aqueous solution containing a zinc salt and an aluminum salt with an aqueous solution containing a surfactant. The method according to claim 6 , wherein the surfactant is an anionic surfactant and/or a cationic surfactant. The method according to claim 6 or 7 , wherein the aqueous solution containing a surfactant further contains an oxoacid salt. The method according to any one of claims 6 to 8 , wherein in the mixing step, the pH is adjusted to 9 to 12 during mixing. The method according to claim 6 , further comprising the step of stirring the mixed aqueous solution after the mixing step. 1. A method for adsorbing volatile sulfur compounds in a liquid phase, comprising:
A method comprising the step of contacting, in the liquid phase, volatile sulfur compounds in the liquid phase with the adsorbent for volatile sulfur compounds in the liquid phase according to any one of claims 1 to 4 . The method of claim 11 , wherein the contacting step is carried out at 0 to 50°C.

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