JP2014152337A - Precipitation method of metallic silver, coated silver fine particle, thin wire-like coated metallic silver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new precipitation method capable of precipitating metallic silver from an aqueous phase, etc., and a method capable of controlling morphology of metallic silver to be precipitated when the metallic silver is precipitated by the new precipitation method.SOLUTION: In a mixed phase comprising: a compound including silver; a polar molecule; and a polar solvent, the compound including silver is decomposed to precipitate metallic silver. The compound including silver is a compound including silver having 0.1 g or less of a solubility at a room temperature relative to 100 g of the polar solvent.

Description

  The present invention relates to a means for depositing various forms of metallic silver from an aqueous phase and the like, and a metallic silver having various forms deposited by the means.

  Conventionally, metallic silver is known to have a high bactericidal effect against bacteria and viruses, and various forms of metallic silver are used to utilize this effect. In recent years, metallic silver is not easily oxidized even in an atmospheric environment and can exist stably in a metallic state, and high electrical conductivity, a high self-diffusion coefficient, etc. are used to make a conductive material in silver paste, especially at low temperatures. Silver fine particles for the purpose of forming conductive wiring are attracting attention. Furthermore, attempts have been made to form a good transparent conductive film by dispersing fine-line (wire-like) metallic silver in a resin.

  The metal silver used in such applications is generally required to have a high specific surface area in order to reduce the cost and develop the desired properties. In other words, in metallic silver used for sterilization, the effect depends on the surface area of metallic silver, and metallic silver having a high specific surface area in order to reduce the amount of relatively expensive metallic silver used. Is desired. In addition, it is desirable that metallic silver used as a conductive material in a silver paste be easily produced in bulky silver particles for low cost and high functionality. In addition, silver fine particles used for wiring formation at low temperature generally have a high specific surface area because the particle size is small and high surface energy promotes sintering between particles at low temperature. Fine particles are desired. Even in the case of fine-line metal silver, in order to form a particularly good transparent conductive film, metal silver having a small cross-sectional area and a long and high specific surface area is required.

  Conventionally, when trying to obtain metallic silver with various specific forms and high specific surface area, generally, existing silver ions such as silver nitrate and silver chloride are dissolved, and silver ions present are reduced with some reducing agent. Then, it was usual to deposit as metallic silver of a desired form (patent documents 1 to 3). In particular, in the production of fine silver fine particles, a method of aggregating atomic silver in a vacuum to form silver fine particles is also known (Patent Document 4).

  In contrast, the present inventor used silver oxalate solubilized in a predetermined organic solvent and the like to agglomerate silver atoms generated by thermally decomposing silver oxalate and the like to form fine silver Technology for producing fine particles has been developed (Patent Documents 5 and 6). According to this technique, silver atoms generated by dissociation from the raw material compound do not pass through the state of silver ions in the process of forming silver fine particles, so it is necessary to mix a reducing agent for reducing silver ions. Therefore, it is possible to produce uniform silver fine particles by a simple method.

Special table 2012-509396 gazette JP 2012-180589 A JP 2012-140701 A JP 2002-121437 A JP 2010-265543 A JP 2012-162767 A

  As described above, when reducing silver ions present in an aqueous solution to precipitate metallic silver, it is essential to mix the reducing agent for the silver ions with the aqueous solution and cause a reaction to reduce the silver ions. Become. In such a metal silver precipitation reaction using a reducing agent, a change occurs in the form of metallic silver deposited due to fluctuations in the concentration of the reducing agent, etc. It may be difficult to cause precipitation. In particular, when metallic silver is precipitated on a large scale in an industrial production process, there is a problem that this tendency becomes remarkable.

Further, when aggregating atomic silver in a vacuum, since the reduction reaction is not involved, the above problem does not occur, but a problem in terms of cost arises.
Moreover, the substance which can be used as a reaction medium was also limited about the method of producing | generating metallic silver using the silver atom produced by thermally decomposing the compound containing silver, such as silver oxalate.
Therefore, the problem to be solved by the present invention is to provide a novel precipitation method for precipitating metallic silver from an aqueous phase or the like. Another object of the present invention is to provide a method capable of controlling the form of metallic silver deposited when metallic silver is deposited by this method. Moreover, it is providing the metallic silver of the various forms which precipitated with the said precipitation method.

  In order to solve the above-mentioned problems, the present invention provides a deposition of metallic silver including a deposition step of decomposing the silver-containing compound and precipitating metallic silver in a mixed phase containing a silver-containing compound, a polar molecule and a polar solvent. A method for depositing metallic silver, wherein the compound containing silver is a compound containing silver having a solubility at room temperature in 100 g of the polar solvent of 0.1 g or less. According to this method, it is possible to deposit metallic silver having a high specific surface area in a polar solvent without requiring a reducing agent for reducing silver ions.

  The method for producing the mixed phase in the present invention is not particularly limited, and can be obtained by mixing a compound containing at least the silver and a polar molecule into a liquid phase containing a polar solvent. It is also possible to obtain the above-mentioned compound containing silver by mixing it with a mixture containing a polar solvent and a polar molecule, and a method in which the compound containing silver, the polar molecule and the polar solvent can form an apparently uniform mixed phase. If it is.

  As described above, the silver-containing compound used in the present invention can be preferably used as long as it does not substantially dissolve in the polar solvent to be used. preferable. In particular, silver oxalate is preferably used because it is difficult to leave a residue in the system when it is decomposed by the method according to the present invention to release silver atoms.

  The polar molecule used in the present invention can be used as long as it can dissolve a hardly-soluble silver-containing compound in a polar solvent, and particularly preferably an alkylamine, alkyldiamine or aminoalcohol having 6 or less carbon atoms. , Those containing any of amino acids and aminoethoxy can be suitably used. The polar solvent used in the present invention is not particularly limited as long as it can dissolve the silver-containing compound having the polar molecule interposed therein. In particular, a polar solvent such as water or alcohol having a hydroxyl group is preferably used.

  According to the present invention, metallic silver can be precipitated in a polar solvent such as an aqueous phase by utilizing thermal decomposition of a compound containing silver. Moreover, the form of the metal silver which precipitates can be controlled by adjusting the conditions in the case of precipitation.

It is a powder X-ray-diffraction pattern of the deposit precipitated in aqueous solution using the silver oxalate which made alkyldiamine act. It is a scanning electron microscope image of the deposit which precipitated in aqueous solution using the silver oxalate which made alkyldiamine act. It is a transmission electron microscope image of the precipitate at the time of depositing the silver oxalate which made alkyldiamine act in gelatin aqueous solution. It is a scanning electron microscope image of the deposit which precipitated in N, N- dimethyl- 1, 3- diaminopropane aqueous solution of each density | concentration of (a)-(c). It is a scanning electron microscope image of the deposit which precipitated in N, N- dimethyl- 1, 3- diaminopropane aqueous solution of each density | concentration of (d)-(f). It is a scanning electron microscope image of the deposit precipitated in N, N-dimethyl-1,3-diaminopropane aqueous solution in the presence of PVP.

  The method for depositing metallic silver according to the present invention comprises thermally decomposing a compound containing silver (hereinafter referred to as “silver compound”) in a polar solvent such as an aqueous phase in the presence of a predetermined polar molecule. It is characterized by depositing metallic silver having various forms. According to the method for depositing metallic silver according to the present invention, it is possible to deposit metallic silver having a high specific surface area in a polar solvent, and the metallic silver deposited by setting various conditions for depositing metallic silver. The form can be adjustable.

  In the present invention, a compound containing silver as a raw material for metallic silver to be deposited is a compound in which silver atoms are bonded in the molecule mainly by covalent bonds, and generates silver ions in a polar solvent. On the other hand, a compound that can be thermally cleaved relatively easily is preferably used. By using such a silver compound, it becomes possible to cause precipitation of metallic silver using a route different from that of metallic silver accompanying reduction of silver ions using ionic silver nitrate or the like.

Since silver compounds with covalently bonded silver atoms in the molecule have a generally lower solubility in polar solvents than ionic compounds, they usually exist as a mixed phase in polar solvents. Therefore, it is difficult to use as a raw material for depositing metallic silver. On the other hand, according to the present invention, by allowing a predetermined polar molecule to intervene in such a silver compound, it is possible to develop solubility in an aqueous phase and the like, and at the same time, the decomposition of the silver compound is facilitated. Has been found to provide a novel method for depositing metallic silver.
That is, in the method for depositing metallic silver according to the present invention, a mixed phase with a polar solvent is formed by mixing and interposing a polar molecule with a silver compound that is difficult to generate silver ions by electrolysis in a polar solvent. In this state, by supplying heat to the silver compound, the silver compound is thermally decomposed to release silver atoms, and the released silver atoms aggregate to deposit metal silver.

  In addition, in the present invention, the above polar molecule is used in combination with a silver compound in advance, and the aqueous phase of the silver compound to be used can also be used by a method such as charging the silver compound into a mixture of the polar molecule and the aqueous phase. It is possible to facilitate the expression of solubility in the silver salt and the decomposition of the silver compound. Although the mechanism by which silver compounds that have essentially no solubility in aqueous phase or the like exhibit solubility due to the presence of polar molecules is not clear, the results of various studies indicate that polar molecules are bound by coordination bonds, etc. It is conceivable that the solubility in a highly polar aqueous phase is increased by modifying the silver compound. Further, it has been clarified so far by the present inventors that decomposition is facilitated by bonding a polar molecule or the like to a silver compound to form a complex or the like (Patent Documents 5 and 6).

In the present invention, as a reaction medium for performing a reaction for thermally decomposing a silver compound to deposit metallic silver, it is typically preferable to use an aqueous phase (aqueous solution) from the viewpoint of cost and environmental load. Also, an organic solvent having polarity such as alcohol, acetone or acetonitrile can be used. In these polar solvents, the presence of polar molecules causes the silver compound to exhibit solubility, and the silver compound can be decomposed at a temperature lower than the original decomposition temperature depending on the polar solvent used. It becomes possible.
In particular, when an aqueous phase, methanol, ethanol, or the like is used as a polar solvent, the solubility of the silver compound in the polar solvent tends to increase, and the reaction medium for depositing various forms of metallic silver Can be preferably used. On the other hand, even in other polar solvents, it is possible to thermally decompose the dissolved silver compound at a relatively low temperature. For example, various forms of metallic silver are deposited in equilibrium with the undissolved silver compound. be able to.

Examples of the form of metallic silver deposited by the method according to the present invention include generally amorphous sponge-like and needle-like ones, and are useful as metallic silver used for sterilization in terms of having a large specific surface area. It is. On the other hand, when metallic silver is deposited in the present invention, the form of metallic silver deposited can be controlled by performing various controls. For example, it is suitable for various individual uses such as fine particles and fine wires (wires). It is possible to easily produce fine metallic silver having
Hereinafter, the method for depositing metallic silver according to the present invention will be described in detail.

(1) About silver compound used to supply silver atoms In the present invention, it is considered that a silver compound is not thermally generated by ionization in a polar solvent but is thermally decomposed by heating or the like. It is characterized by depositing various forms of metallic silver using silver atoms. For this reason, as the raw material for metallic silver in the present invention, those having low solubility in the polar solvent to be used are preferably used. Specifically, the amount dissolved in 100 g of the solvent is 0.1 g or less at room temperature, more preferably A silver compound of 0.01 g or less is preferably used. When a silver compound having high solubility in the polar solvent to be used is used, silver ions generated by ionization of the charged silver compound do not contribute to the precipitation of metallic silver according to the present invention, and the yield of silver is greatly reduced. This is not preferable.

  As a silver compound having low solubility in a polar solvent, for example, in the case of using an aqueous phase, a silver carboxylate in which silver and a carboxylic acid such as acetic acid, oxalic acid, malonic acid, benzoic acid, and phthalic acid are combined, Examples thereof include silver oxide, silver sulfide, silver carbonate, silver thiocyanate, and silver phosphate. Silver halides such as silver chloride and silver bromide also generally have low solubility in the aqueous phase, but if ions or molecules that serve as ligands are present, they dissolve by forming complex ions. For this reason, care must be taken in relation to the polar molecules used.

  Among the above, silver carboxylate is particularly preferable as a silver raw material in the present invention because it is difficult to release silver ions by ionization. In particular, silver oxalate that is silver carboxylate is particularly preferable because it can be pyrolyzed relatively easily to release silver atoms, and a pyrolysis by-product is released as carbon dioxide out of the reaction system. used. On the other hand, it is also possible to make adjustments such as using other silver compounds alone or mixed with a plurality of silver compounds for the purpose of controlling the precipitation reaction of silver and controlling the form of metallic silver to be precipitated. . Carboxylic acids are also expected to function as protective molecules for stably holding the fine metal silver produced.

(2) Polar molecules for imparting solubility in a polar solvent to the silver compound As described below, the polar molecules used in the present invention provide the silver compound with solubility in the polar solvent, and at the same time, It is thought to play an important role in controlling the decomposition temperature and the form of metallic silver deposition. The polar molecule used in the present invention substantially expresses solubility in a polar solvent by modifying the silver compound by forming a complex compound or the like in relation to the silver compound or polar solvent used. As long as it can form a mixed phase containing a polar molecule and a polar solvent, it can be used by selecting from various polar molecules according to the use of metallic silver deposited without any particular limitation.

  The “mixed phase” is not particularly limited as long as the three components constitute a single phase. For example, microscopically, a complex compound containing a silver compound and a polar molecule is dispersed in a polar solvent. , Including the case of fluctuations in macroscopic composition. Further, for example, even when a large amount of silver compound is introduced into the system and a silver compound that does not dissolve in the mixture remains, the presence of the three-component mixed phase in the system makes it possible to The invention can be successfully implemented.

As such a polar molecule, for example, an organic compound having an amino group (NH ₂ ) in the molecule can be preferably exemplified. For example, as described in the above cited references 5, 6 and the like, molecules having an amino group easily form a complex compound by forming a coordinate bond via the amino group to the silver atom in the silver compound, It is known that the structure of a silver compound is chemically unstable, causing thermal decomposition at a temperature lower than the original decomposition temperature. Also in the present invention, by causing a polar compound containing at least one amino group to intervene in the silver compound, solubility in a polar solvent is expressed and thermal decomposition is caused at a temperature lower than the original decomposition temperature of the silver compound. Therefore, it is considered that a complex compound or the like is formed through a coordination bond between the amino group and the silver atom.

The amino group is preferably a primary amino group RNH ₂ (R is a hydrocarbon chain), but a secondary amino group R ¹ R ² NH (R ¹ and R ² are the same in a hydrocarbon chain. Or may be different), coordination to silver atoms in the silver compound is possible. On the other hand, when it becomes a tertiary amino group, it may become difficult to coordinate to a silver atom spatially.

  As the polar molecule preferably used in the present invention, the hydrocarbon chain connected to the amino group is relatively short, for example, those having 6 or less carbon atoms, more preferably those having 5 or less carbon atoms, And those having a plurality of amino groups, and those having a polar group such as a hydroxyl group (—OH) or a carboxyl group (—COOH). Specifically, short-chain alkylamines, alkyldiamines having two amino groups in one molecule, aminoalcohols having amino groups and hydroxyl groups, amino acids having amino groups and carboxyl groups, etc. Can be mentioned. Further, aminoethoxys having an amino group and a hydroxyl group and an ether bond in the alkyl chain can be exemplified.

The reason why the polar molecule having the above structure is preferably used in the present invention is not clear, but by using the polar molecule having such a structure, when the amino group is coordinated to the silver atom in the silver compound, etc. Since a relatively hydrophilic portion appears on the surface, it is considered that it contributes to the improvement of the solubility in an aqueous phase as a reaction medium. In the present invention, a specific polar molecule is selected according to the form of metallic silver to be precipitated, or a mixture of a plurality of polar molecules is used to improve the solubility in the reaction medium and the decomposability of the silver compound. It becomes possible to control.
Specific examples of short-chain alkylamines that can be preferably used include amylamine, 2-ethoxyethylamine, 4-methoxybutylamine, diisopropylamine, butylamine, diethylamine, propylamine, isopropylamine, ethylamine, dimethylamine, and the like that are industrially available. Possible and desirable to use.

  Examples of alkyldiamines that can be preferably used include, for example, ethylenediamine, N, N-dimethylethylenediamine, N, N′-dimethylethylenediamine, N, N-diethylethylenediamine, N, N′-diethylethylenediamine, and 1,3-propane. Diamine, 2,2-dimethyl-1,3-propanediamine, N, N-dimethyl-1,3-diaminopropane, N, N′-dimethyl-1,3-diaminopropane, N, N-diethyl-1, 3-diaminopropane, 1,4-diaminobutane, 1,5-diamino-2-methylpentane, 1,6-diaminohexane, N, N′-dimethyl-1,6-diaminohexane, 1,7-diaminoheptane 1,8-diaminooctane and the like, but are not limited thereto.

  Examples of amino alcohols that can be preferably used include methanolamine, 2-aminoethanol, 1-amino-2-butanol and the like, and diethanolamine having a plurality of hydroxyl groups. As aminoethoxys, 2- (2-aminoethoxy) ethanol is easily available and is typically used. In addition, as amino acids that can be preferably used, various amino acids such as glycine, β-alanine, and γ-aminobutyric acid can be used as appropriate, but when β-amino acids and γ-amino acids are used in comparison with α-amino acids, There is a tendency to facilitate decomposition.

  As a method of interposing the above polar molecules with respect to the silver compound, a predetermined amount of polar molecules are mixed with the silver compound in advance to form a complex compound and the like, and then an aqueous phase that serves as a reaction medium during thermal decomposition Alternatively, the silver compound may be dissolved in a polar solvent such as, and then thermally decomposed by heating. This method is preferable in that homogeneous metal silver can be easily obtained even when a large amount of metal silver is deposited. This is because, in this method, a homogeneous silver compound and a complex compound of polar molecules are supplied into the reaction medium, and these undergo thermal decomposition at a specific temperature according to the components of each complex compound during heating. For this reason, it is considered that homogeneous silver atoms can be generated stably.

  By this method, when the complex compound obtained by interposing a polar molecule with a silver compound is dissolved in the reaction medium, the ratio of the polar molecule mixed with the silver compound is changed to the complex compound with the silver compound. Smooth dissolution can be performed by using more than the equivalent amount for forming. This is presumably because some of the polar molecules are dissociated from the complex compound in the reaction medium. Although depending on the amount of the reaction medium to be used, it is generally possible to smoothly dissolve in the reaction medium by mixing 4 or more equivalents of polar molecules in the silver compound.

  By mixing polar molecules effective for the silver compound and stirring at an appropriate temperature, the solid silver compound generally changes to a paste and becomes soluble in a polar solvent. When metal silver is deposited by this method, a silver compound made into a paste or the like in a reaction medium (polar solvent) maintained at a temperature equal to or lower than the thermal decomposition temperature of a complex compound or the like produced by mixing a silver compound and a polar molecule And stirring to form a uniform mixed phase, and then the silver compound is preferably thermally decomposed by heating. In this way, even when metal silver is deposited on a large scale, each silver compound is decomposed only by temperature, so that uniform metal silver can be deposited. On the other hand, in the case of causing thermal decomposition at a temperature higher than the thermal decomposition temperature of a complex compound or the like, the silver compound in a paste form or the like is put into a reaction medium maintained at a predetermined temperature to thermally decompose the silver compound. Is possible.

On the other hand, according to the purpose such as form control of the deposited silver metal, a mixed solution in which a predetermined amount of polar molecules is dissolved in the reaction medium is prepared in advance, and a silver compound is added to the mixture heated to a desired temperature. The silver metal can also be precipitated by the addition. According to this method, the charged silver compound is dissolved by generating a polar molecule, a complex compound, and the like in the reaction medium, and then the complex compound and the like are thermally decomposed, so that silver atoms are released and metal silver is formed. It is thought that it precipitates. According to this method, it becomes possible to deposit metallic silver at a temperature equal to or higher than the thermal decomposition temperature inherent in the complex compound to be produced, and is effective as a method for controlling the form of precipitated metallic silver.
In addition, metal silver is deposited by an appropriate method such as depositing a silver compound in which a complex compound or the like is previously formed with a predetermined polar solvent into a reaction medium containing the same or different polar solvent. It is possible to make it.

(3) Polar solvent (reaction medium) for precipitation of metallic silver In the present invention, as a reaction medium for thermally decomposing a silver compound in the presence of a polar molecule to deposit metallic silver, a silver compound and a polar molecule are particularly preferred. It is preferable to use a complex such as a complex compound having a predetermined solubility. In addition to the solubility of the complex such as the complex compound, the decomposition start temperature of the complex also changes depending on the type of the reaction medium. Substances to be combined and combinations thereof can be selected.

  In the present invention, from the viewpoint of precipitating metallic silver in a reaction medium mainly having a polarity such as an aqueous phase, typically a plurality of polar functional groups as described above are used as polar molecules intervening in a silver compound. The organic compound containing is preferably used. For this reason, as a reaction medium, a thing with high solubility with the polar molecule to be used is used preferably. In addition, the reaction medium can be appropriately determined in consideration of the influence of the complex such as a complex compound on the thermal decomposition temperature, the vapor pressure and the boiling point of the reaction medium.

Typically, as a reaction medium in the present invention, in addition to using an aqueous phase, it is desirable to use an organic solvent having polarity such as alcohol, acetone, and acetonitrile. In these polar solvents, a complex such as a complex compound of a silver compound and a polar molecule used in the present invention exhibits a certain solubility, and may undergo thermal decomposition at a temperature of about 30 to 100 ° C. Therefore, it can be preferably used as a reaction medium for depositing metallic silver.
In particular, when a substance having a hydroxyl group such as an aqueous phase, methanol or ethanol and a relatively small molecular weight is used as a reaction medium, a complex such as a complex compound of a silver compound and a polar molecule tends to have high solubility. Since these are seen, those which are used alone or mixed with other substances are preferably used.

(4) Form control of metallic silver deposited In the metallic silver deposition method according to the present invention, it is possible to easily control the form of metallic silver deposited by controlling the process of depositing metallic silver. is there. In other words, in the reaction medium when metallic silver is deposited, so-called a so-called role that suppresses excessive growth so that the deposited metallic silver does not exceed a predetermined size, and especially suppresses growth in a predetermined orientation. The presence of molecules corresponding to “capping molecules” makes it possible to control the form of precipitated silver metal. Similarly to the case of precipitation from silver ions or the like, a so-called “template molecule” is allowed to be present in the reaction medium, so that metallic silver in a desired form can be deposited.

  As the capping molecule, in addition to dissolving a molecular species suitable for a predetermined shape control purpose in the reaction medium, in particular, the kind of polar molecule used for the expression of the solubility in the reaction medium by interposing it in the silver compound as described above, It is also effective to control the form of the metallic silver that is used as a capping molecule by adjusting the concentration. Although it is not clear why the polar molecule used functions as a capping molecule, the polar molecule desirably used in the present invention contains an amino group, and this amino group is bonded to a silver atom in the silver compound by a coordination bond, It is considered that the bond with the silver atom is maintained even after the silver compound is thermally decomposed. For this reason, the polar molecules used are bonded to the silver atoms generated by the thermal decomposition of the silver compound in the present invention. For this reason, the mobility of the silver atoms is limited, or the specific surface of the deposited metal silver surface is limited. It is assumed that polar molecules function as capping molecules by a mechanism such as the presence of high-density polar molecules on the crystal orientation plane.

  In particular, as shown by the following examples and the like, in the deposition of metallic silver according to the present invention, metallic silver having a strong anisotropy can be deposited by the polar molecules acting as capping molecules. That is, in the case where fine linear metallic silver having a strong anisotropy is precipitated from silver ions, a chain molecule having a strong polarity such as PVP is interposed as described in Patent Documents 1 to 3, and the like. It is necessary to perform precipitation as follows. On the other hand, when depositing metallic silver according to the present invention, fine metallic silver can be deposited without interposing template molecules, which is considered to be the effect of capping by the polar molecules used. .

  On the other hand, it is possible to obtain isotropic metallic silver such as fine particles by allowing a molecule having a relatively large molecular weight to be present in the reaction medium as a capping molecule. When such molecules are present in the reaction medium, the mobility of the silver atoms is restricted by the adhesion of these molecules to the silver atoms generated by thermal decomposition of the silver compound, and the aggregation of the silver atoms. This is considered to be because a film is formed on the surface of the silver fine particles to be generated, and it becomes difficult to grow a certain particle or more.

  In particular, when thin-line metallic silver is deposited, it is also effective to dissolve a water-soluble chain polymer in the reaction medium and use it as a template molecule that selectively deposits metallic silver on this polymer. is there. As such a chain polymer serving as a template molecule, a polar polymer having a polar group in the polymer is preferable, and polymers such as polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyethyleneimine, polyethylene oxide, and gelatin are preferably used. .

(5) Recovery of precipitated metallic silver The metallic silver deposited according to the present invention is highly protected in the polar solvent used because its surface is protected by commonly used polar molecules and other capping molecules. It can be monodispersed in concentration. For this reason, by taking out the protective film on the surface of the deposited silver metal without damaging it, or by substituting with an appropriate protective molecule, the aggregation of the deposited silver metal is prevented, and the state is maintained in various applications. Can be used.
Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
As a silver compound, 0.48 g (1.6 mmol) of silver oxalate synthesized from silver nitrate (Kanto Chemical, primary) and ammonium oxalate monohydrate or oxalic acid dihydrate (Kanto Chemical, special grade) As polar molecules to intervene, 12.5 mmol of each listed in Table 1 was added and stirred at room temperature for 10 minutes. Thereafter, while adding 4 ml of distilled water and stirring, the mixture was immediately heated to 100 ° C. and stirred for 2 hours to examine the solubility of silver oxalate and the possibility of precipitation of metallic silver. For comparison, only silver oxalate was added to distilled water, heated to 100 ° C., and stirred for 2 hours.

  The results of the above examination are shown in Table 1. In Table 1, in the solubility of the added silver oxalate in water, “◎” indicates that the total amount of the added silver oxalate is rapidly dissolved, “△” indicates that a part of the silver oxalate is dissolved, and dissolution. Those not recognized by “×” are indicated by “x”. Further, regarding the precipitation of metallic silver, “◎” indicates that good precipitation was observed, “◯” indicates that precipitation was observed, “Δ” indicates that precipitation was slightly observed, and no precipitation was observed. The thing was shown by "x".

  As is apparent from Table 1, the silver oxalate used does not dissolve in water at 100 ° C. and does not cause metallic silver to precipitate due to decomposition, whereas the material previously mixed with polar molecules has significant water. As well as the solubility in the water, it decomposed at a low temperature of about 100 ° C. to give a gray suspension. As shown below, the gray suspension is accompanied by the precipitation of fine metallic silver, and the presence of polar molecules chemically activates silver oxalate, resulting in solubility in water and at low temperatures. It was shown to decompose and release silver atoms. In particular, the effect was remarkably seen in alkyldiamines containing two amino groups in the molecule, aminoethanols having amino groups and hydroxyl groups, and aminoethoxyethanols.

  The aqueous solution in which metallic silver is deposited using N, N-dimethyl-1,3-diaminopropane (Tokyo Kasei, special grade) as described above is added with 4 ml of methanol (Kanto Chemical Co., Ltd., first grade) and centrifuged to obtain a precipitate. Got. The obtained precipitate was dried and then analyzed by a powder X-ray diffractometer (Rigaku MiniFlex II) and a scanning electron microscope (JEOL JEM7600). FIG. 1 shows the result of powder X-ray diffraction of the precipitate. FIG. 2 shows the results of observation with a scanning electron microscope. From the results of the analysis, it was considered that the crystal phase contained in the precipitate was metallic silver. Also, from the results of observation with a scanning electron microscope, most of the precipitate is amorphous metal silver having a size of about several hundreds of nanometers, and a part of which is thin metal silver with a length of about several μm. It was considered.

[Example 2]
Next, 0.48 g (1.6 mmol) of silver oxalate used in Example 1 is used to clarify a reaction medium that can be used when metal silver is precipitated using a mixture of silver oxalate and polar molecules. After adding 1.28 g (12.5 mmol) of N, N-dimethyl-1,3-diaminopropane and stirring for 10 minutes, distilled water, methanol, ethanol, acetonitrile and benzene were added as shown in Table 2. Each 4 ml was adjusted. When each mixture was heated to the temperature shown in Table 2 and stirred for 2 hours, the solubility of silver oxalate and the possibility of precipitation of metallic silver were examined.

  The results of the above examination are shown in Table 2. In Table 2, regarding the solubility of the input silver oxalate, “◎” indicates that the total amount of the added silver oxalate is rapidly dissolved, and “○” indicates that a portion of the total amount is dissolved. Is indicated by “Δ”, and those where dissolution is not observed are indicated by “x”. Further, regarding the precipitation of metallic silver, “も の” indicates that good precipitation was observed, and “◯” indicates that precipitation was observed.

  As shown in Table 2, for silver oxalate mixed with N, N-dimethyl-1,3-diaminopropane as a polar molecule, a remarkable solubility is observed in addition to water, particularly in alcohol, and a solvent containing a hydroxyl group. It was inferred that the solubility is shown. Moreover, in the reaction medium in which silver oxalate was dissolved, it was shown that silver oxalate decomposes at a low temperature of about 60 to 100 ° C. to produce metallic silver. On the other hand, when benzene, which is a nonpolar solvent, is used, the dissolution of silver oxalate is not observed, but the added silver oxalate decomposes in a state of phase separation with the aqueous phase to produce metallic silver. It was observed.

[Example 3]
In the precipitation of metallic silver accompanying the thermal decomposition of a silver compound in a polar solvent such as an aqueous phase as clarified above, an attempt was made to control the form of the metallic silver deposited.
To 0.48 g (1.6 mmol) of silver oxalate used in Example 1, 1.28 g (12.5 mmol) of N, N-dimethyl-1,3-diaminopropane was added and stirred for 10 minutes. On the other hand, 4 ml of an aqueous solution in which gelatin (Kanto Chemical) was dissolved in distilled water at a concentration of 40 mg / ml was added to prepare a mixed aqueous solution. When this aqueous solution was heated to 100 ° C. and stirred for 2 hours, the color of the solution changed to yellow and then gradually changed to red, and a stable dispersion was obtained. After completion of the stirring, the reaction solution was allowed to cool naturally, and 4 ml of 3.1 mmol / l N, N-dimethyl 1,3-diaminopropane aqueous solution was added and centrifuged. Further, 4 ml of distilled water was added to the resulting precipitate and redispersed, followed by centrifugation, and the resulting precipitate was naturally dried to obtain a product.

  In FIG. 3, the result of having observed the sample obtained above with the transmission electron microscope (JEOL JEM2100F) is shown. As shown in FIG. 3, the metallic silver obtained as a precipitate above had a fine particle shape with a particle size of about 10 to 30 nm. Further, as apparent from FIG. 3, each particle is observed at a predetermined interval, so that each particle is considered to be a coated silver fine particle in which silver fine particles are coated with a protective film.

  As a result of applying the aqueous solution in which the silver fine particles were dispersed on the resin substrate and baking at 100 ° C. for 60 minutes, a conductive silver thin film was obtained. Also, in the thermogravimetric / mass simultaneous analyzer (TG-Mass / thermogravimetric analysis (TG): TA Instruments SDT Q600, mass spectrometry (Mass): JEOL JSM-Q1050GC, EI and photoionization, under helium flow) As a result of heating and measuring the silver fine particles, it was inferred that the coating on the surface of the silver fine particles contained the above-mentioned N, N-dimethyl-1,3-diaminopropane and gelatin, and the dioxide caused by oxalic acid. Carbon was detected.

[Example 4]
In the precipitation of metallic silver accompanying the thermal decomposition of a silver compound in a polar solvent such as an aqueous phase as clarified above, another form control of metallic silver deposited was attempted. Specifically, an attempt was made to control the form of metallic silver deposited by the concentration of N, N-dimethyl-1,3-diaminopropane, which is a polar molecule intervening in the silver compound. Further, in order to control the temperature at the time of precipitation, in an aqueous N, N-dimethyl-1,3-diaminopropane solution maintained at a predetermined temperature (80 ° C.) higher than the temperature at which decomposition of silver oxalate, which is a silver compound, occurs. In this study, silver oxalate was added to the test piece.

  2. N, N-dimethyl-1,3-diaminopropane 0.64 g (6.25 mmol), 1.28 g (12.5 mmol), 1.92 g (18.3 mmol), 2.56 g (25.0 mmol); 20 g (31.3 mmol) and 3.84 g (47.5 mmol) were weighed, mixed with 2.8 ml of distilled water, mixed, 2.23 mol / l, 4.46 mol / l, 6.54 mol / l, 8 N, N-dimethyl-1,3-diaminopropane aqueous solutions having respective concentrations of .93 mol / l, 11.2 mol / l and 17.0 mol / l were prepared. After each aqueous solution was heated to 80 ° C., 0.48 g (1.6 mmol) of silver oxalate obtained in Example 1 was added to each aqueous solution. When stirred after the addition, silver oxalate immediately dissolved in the aqueous solution to form a uniform aqueous solution, after which the color of the solution changed from yellow to red and finally to a black suspension. After 30 minutes, the reaction solution was allowed to cool naturally to complete the reaction. In order to take out the suspension in the aqueous solution, 4 mL of 3.1 mmol / l N, N-dimethyl 1,3-diaminopropane aqueous solution was added and centrifuged. Further, 4 ml of distilled water was added to the resulting precipitate and redispersed, followed by centrifugation. The obtained precipitate was naturally dried and observed with a scanning electron microscope (JEOL JEM7600).

  FIG. 4 shows a scanning electron microscope image of metallic silver precipitated in the N, N-dimethyl-1,3-diaminopropane aqueous solution having each concentration described above. As shown in FIG. 4, even when silver oxalate is added to an N, N-dimethyl-1,3-diaminopropane aqueous solution, N, N-dimethyl-1,3-diaminopropane and oxalic acid in advance. The same precipitate was produced as when silver was mixed and dissolved in water. In addition, when the form of the precipitate changes depending on the concentration of N, N-dimethyl-1,3-diaminopropane in the aqueous solution and the concentration is about 4.46 mol / l, a fine fine wire shape (wire shape) On the other hand, when the concentration of N, N-dimethyl-1,3-diaminopropane was increased, there was a tendency for plate-shaped metallic silver to increase.

  Thus, the reason why the metallic silver deposited in this example exhibits a highly anisotropic shape is that N, N-dimethyl-1,3-diaminopropane present in the aqueous solution is deposited on the surface of the metallic silver being deposited. This is considered to be a result of hindering crystal growth in a specific orientation due to adhesion or the like. In particular, in the present example, it is possible to deposit metal silver with very high anisotropy despite the absence of template molecules that promote the precipitation of fine-line metal silver. This suggests that precipitation by a different path from that of metallic silver using silver ions occurs.

  In addition, the thin-line silver obtained above has hydrophilicity such as being well dispersed in an aqueous phase, alcohol, or the like, and it was considered that a hydrophilic protective coating was formed on the surface. Precipitation in a thermogravimetric / mass simultaneous analyzer (TG-Mass / thermogravimetric analysis (TG): TA Instruments SDT Q600, mass spectrometry (Mass): JEOL JSM-Q1050GC, EI and photoionization, helium flow) As a result of heating and measuring the deposited metallic silver, it was inferred that the used N, N-dimethyl-1,3-diaminopropane was present on the surface of the deposited metallic silver.

[Example 5]
In the precipitation of metallic silver accompanying the thermal decomposition of a silver compound in a polar solvent such as an aqueous phase as clarified above, another form control of metallic silver deposited was attempted. Specifically, precipitation of metallic silver in a state in which polyvinyl pyrrolidone generally used as a template material was mixed during the precipitation of thin linear silver from an aqueous silver nitrate solution was examined.

  N, N-dimethyl-1,3-diaminopropane 1.28 g (12.5 mmol), polyvinylpyrrolidone K30 (molecular weight 40000, Tokyo Kasei) 1.2 g, distilled water 2.8 ml, 0.1 N nitric acid (Tokyo Kasei) ) A mixed aqueous solution was prepared by adding 0.1 ml of an aqueous solution. After heating this aqueous solution to 80 ° C., 0.48 g (1.6 mmol) of silver oxalate obtained in Example 1 was added. When stirred after the addition, silver oxalate immediately dissolved in the aqueous solution to form a uniform aqueous solution, after which the color of the solution changed from yellow to red and finally to a black suspension. After 30 minutes, the reaction solution was allowed to cool naturally to complete the reaction. In order to take out the suspension in the aqueous solution, 4 mL of 3.1 mmol / l N, N-dimethyl 1,3-diaminopropane aqueous solution was added and centrifuged. Further, 4 ml of distilled water was added to the resulting precipitate and redispersed, followed by centrifugation. The obtained precipitate was naturally dried and observed with a scanning electron microscope (JEOL JEM7600).

  FIG. 5 shows a scanning electron microscope image of metallic silver precipitated in an aqueous solution of N, N-dimethyl-1,3-diaminopropane mixed with polyvinylpyrrolidone. Even when polyvinylpyrrolidone was mixed, it was observed that fine fine-line metallic silver was deposited.

  As described above, the method for depositing metallic silver according to the present invention can easily deposit metallic silver having a large specific surface area in a polar solvent such as an aqueous phase. Moreover, it is possible to control the form of metallic silver to be deposited, and it is possible to provide metallic silver having various forms and characteristics that have been difficult to provide in the past.

Claims (9)

  A method of depositing metallic silver comprising a precipitation step of decomposing the compound containing silver and precipitating metallic silver in a mixed phase comprising a compound containing silver, a polar molecule and a polar solvent, wherein the compound containing silver is A method for depositing metallic silver, which is a compound containing silver having a solubility at room temperature in 100 g of the polar solvent of 0.1 g or less.   2. The metallic silver according to claim 1, wherein the mixed phase is obtained by mixing a compound containing at least the silver-containing compound and a polar molecule into a liquid phase containing a polar solvent. Precipitation method.   The method for depositing metallic silver according to claim 1, wherein the mixed phase is obtained by mixing the compound containing silver with a mixture containing a polar solvent and a polar molecule.   The method for depositing metallic silver according to claim 1, wherein the silver-containing compound is silver carboxylate.   The method for depositing metallic silver according to claim 4, wherein the compound containing silver is silver oxalate.   The method for depositing metallic silver according to any one of claims 1 to 5, wherein the polar molecule includes any one of alkylamine, alkyldiamine, aminoalcohol, amino acid, and aminoethoxy having 6 or less carbon atoms. .   The method for depositing metallic silver according to claim 1, wherein the polar solvent contains a solvent having a hydroxyl group.   Coated silver fine particles, wherein metallic silver particles having an average particle size of 50 nm or less are coated with a coating containing an alkyldiamine and gelatin.   A fine-line-shaped metal silver having a diameter of 100 nm or less and a fine-line metal silver having a length of 10 times or more of the diameter is coated with a coating containing an alkyldiamine.