JP2016000841A - Method for producing purified aqueous dispersion of nano metal particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method for producing a purified aqueous dispersion of nano metal particles without occurrence of flocculation or fusion of the metal nano metal particles.SOLUTION: The purified aqueous dispersion of nano metal particles can be obtained simply without occurrence of flocculation or fusion of the metal nano particles by contacting an aqueous dispersion (A) of nano metal particles containing inorganic acid ions and a water-absorbing resin so that the water-absorbing resin absorbs the liquid, and thereafter redispersing the nano metal particles on the water-absorbing resin (B) by using water and an organic solvent.

Description

  The present invention relates to a method for producing a purified aqueous dispersion of nano metal particles.

  Metal nanoparticles have been focused on functions such as melting point reduction and high catalyst efficiency derived from the size of the specific surface area, and are being studied for applications in the formation of conductive paths, catalysts, bactericides, sensors, etc. Silver has already been put into practical use in some fields such as a coating film for electromagnetic wave shielding of mobile phones.

  Many of these metal nanoparticle synthesis methods are based on a salt-reduction reaction in the liquid phase. In this reaction, unreacted raw materials such as a protective agent and a reducing agent, by-products, and ionic components remain unavoidably, These residues are considered to cause deterioration and deterioration of functions including conductivity.

  However, in the production of various types of metal nanoparticles, various studies on the particle formation process are being promoted. On the other hand, regarding the separation and purification methods, there are few studies other than known methods such as drying, centrifugation, and ultrafiltration. is there.

  Among these, in the simplest drying, there is a problem that the non-volatile impurities that the metal nanoparticles aggregate or fuse cannot be removed. Further, in the centrifugal separation, the disadvantage that the metal nanoparticles are difficult to settle is unavoidable. Since centrifugal force G that can be realized in large-scale production does not settle, a method of adding a poor solvent to soft agglomerate and sedimenting as temporary giant particles is known, but a large amount of organic solvent is required. As a result, the aggregation of the metal nanoparticles is strengthened or fused, and as a result, a crushing step is required separately, and the equipment cost is high (Patent Document 1).

  In ultrafiltration, there is a problem that a large amount of water is used and a large amount of waste water is used, a long time is required for filtration, and the filtration membrane needs to be frequently maintained for stable purification (Patent Document 2). ~ 3).

  In this way, it is purified without agglomerating or fusing metal nanoparticles from an aqueous dispersion of nanometal particles in which unreacted raw materials such as a protective agent and a reducing agent, by-products and ionic components inevitably remain. In addition, there is no simple method for obtaining an aqueous dispersion of nano metal particles.

JP 2010-7124 A JP 2003-103158 A JP 2010-209421 A

  In view of the above circumstances, the problem to be solved by the present invention is to provide a simple method for obtaining a purified aqueous dispersion of nano metal particles without aggregating or fusing metal nanoparticles.

  As a result of intensive studies to solve the above problems, the inventors of the present invention brought an aqueous dispersion of nano metal particles containing at least an inorganic acid ion that is a counter anion of a raw material into contact with a water absorbent resin. Only the non-volatile component mainly composed of nano metal particles and a protective agent having strong interaction with the nano metal particles is left on the surface of the water absorbent resin, and the inorganic acid ions and other inevitable components described above are mixed with the liquid medium inside the water absorbent resin. By absorbing it, it is found that the nanometal particles can be selectively recovered without agglomeration or fusion, and the non-volatile content on the surface of the water-absorbent resin is dispersed again in the liquid medium, so that the inevitable components as described above can be obtained. The present inventors have found that a purified aqueous dispersion of nano metal particles that does not contain can be easily obtained, and completed the present invention.

  That is, the present invention relates to the nanometal particles on the water absorbent resin (B) after bringing the aqueous dispersion of nanometal particles (A) containing inorganic acid ions into contact with the water absorbent resin (B) to absorb the liquid. Is redispersed using water and an organic solvent, and the manufacturing method of the refined nano metal particle aqueous dispersion (D) is provided.

  Since the present invention uses a water-absorbent resin, in the relatively short time, only the non-volatile content mainly composed of nanometal particles and a protective agent having a strong interaction with them is left on the surface of the water-absorbent resin. The above inevitable components can be absorbed inside the water-absorbent resin together with the liquid medium, and can be selectively recovered without agglomerating or fusing the nanometal particles. For this reason, there is an especially remarkable effect that the purified nano metal particle aqueous dispersion can be easily obtained simply by dispersing the non-volatile content recovered from the surface of the water-absorbent resin into the liquid medium again.

  In the present invention, the nanometal particle aqueous dispersion (A) containing inorganic acid ions and the water absorbent resin (B) are brought into contact with each other to absorb the liquid, and then the nanometal particles on the water absorbent resin (B) are The present invention relates to a method for producing a purified aqueous dispersion of nanometal particles (D) that is redispersed using water and an organic solvent.

<Nanometal particle aqueous dispersion containing inorganic acid ions>
In the present invention, the “inorganic acid ion” varies depending on the metal compound used in the production of the nanometal particle dispersion described later, and thus cannot be defined unconditionally, but includes chlorine ion, nitrate ion, sulfate ion and the like.
In the present invention, the nano metal particles are nanoparticles having a particle size of 1 to several hundred nanometers. Nanometals have a much higher specific surface area than bulk metals, so they tend to fuse with each other to reduce surface energy, and particles fuse with each other at temperatures much lower than the melting point of bulk metals. . Due to the nature of these nanometals, application to catalysts, electronic materials, magnetic materials, optical materials, various sensors, color materials, medical examination applications and the like is expected. Here, a protective agent as described later (hereinafter referred to as protection for nanometal particles) plays a role of forming micelles as a place for nanometal particle growth and also prevents fusion of nanometal particles after growth. It may be expressed as an agent).
The protective agent for nano metal particles used in the present invention may be any as long as it is coated with nano metal particles. For example, amine group, carboxyl group, amino group, hydroxy group, thiol group, phosphorus Compounds having functional groups such as acid groups, quaternary ammonium groups, quaternary phosphonium groups, cyano groups, ether groups, thioether groups, disulfide groups, surfactants, amphiphilic polymers, proteins such as gelatin and collagen, Water-soluble polymers such as polyvinyl alcohol and polyvinyl pyrrolidone can be used.
To illustrate some of these more specific examples, a compound (x1) in which polyethylene glycol (b) is bonded to an amino group in polyethyleneimine (a) is linear to the amino group in polyethyleneimine (a). Compound (x2) in which epoxy resin (c) is bonded, and compound (x3) in which polyethylene glycol (b) and linear epoxy resin (c) are bonded to an amino group in polyethyleneimine (a) And one or more compounds (X) selected from the group consisting of: About such a compound, it is already described in Unexamined-Japanese-Patent No. 2010-118168 that it is excellent in the protection function to a metal nanoparticle, and the manufacturing method is also described.
The compounds described in JP 2010-209421 A can also be used.
Further, a (meth) acrylate macromonomer having a polyethylene glycol chain and a (meth) acrylate monomer having a phosphate ester residue represented by -OP (O) (OH) ₂ are represented by -SR (R is , An alkyl group having 1 to 18 carbon atoms, a phenyl group optionally having a substituent on the benzene ring, or a hydroxy group, an alkoxy group having 1 to 18 carbon atoms, an aralkyloxy group having 1 to 18 carbon atoms, Phenyloxy group, carboxy group, carboxy group salt, monovalent or polyvalent alkylcarbonyloxy group having 1 to 18 carbon atoms and monovalent having 1 to 18 carbon atoms, which may have a substituent on the benzene ring Or a chain having a functional group represented by a C1-C8 alkyl group having one or more functional groups selected from the group consisting of polyvalent alkoxycarbonyl groups. (Meth) acrylic polymer (Y) obtained by polymerization in the presence of a transfer agent, or the following general formula (1)
_{X- (OCH 2 CHR 1) n} -O-CH 2 -CH (OH) -CH 2 -S-Z (1)
Wherein (1), X is an alkyl group of _{C 1 ~C 8, R} 1 is a hydrogen atom or a methyl radical, n is an integer indicating the number of repetitions of 2 to 100, _{R 1} is repeated independently for each unit, may be different even in the same, Z is an alkyl group of _C 2 _{-C 12,} an allyl group, an aryl group, an arylalkyl _{group, -R 2 -OH, -R 2 -NHR} 3 , or _-R 2 -COR ₄ (where, _{R 2} is an alkylene chain of _C 2 _{~C 4, R 3} is a hydrogen _atom, an acyl group of C 2 -C _4, alkoxycarbonyl group C 2 -C _4, Or a C ₁ -C ₄ alkyl group or a C ₁ -C ₈ alkoxy group which may have a substituent on the aromatic ring, and R ₄ is a hydroxy group, C ₁ -C ₄ It is alkyl or alkoxy group _C 1 -C ₈ ) Is a group represented by. ] The thioether containing organic compound (Z) etc. which are represented by these are mentioned. In Japanese Patent No. 4697356 and Japanese Patent No. 4784847, it is described that the metal nanoparticle has an excellent protection function, and its production method is also described.

  The metal compound used in the present invention preferably has solubility in a solvent. Specifically, metal salts are preferable, and examples include metal acetates, nitrates, sulfates, chlorides, and acetylacetonates. Of these, nitrate is preferable. Even insoluble salts can be provided with solubility by adding ammonia, amines, or hydrazines or hydroxylamines that also serve as reducing agents as complexing agents. In addition to the above, metal oxides can also be used.

Examples of the metal species of the present invention include so-called transition metal elements. Specifically, industrially useful metal colloids are gold, silver, copper or platinum group elements (ruthenium, rhodium, palladium, Osmium, iridium or platinum) and these are used. The metal species of the present invention includes alloys of these metals, core-shell type particles, and the like.
As the metal compound, for example, when the metal species is gold or platinum, tetrachloroauric acid or tetrachloroplatinum can be used.
For example, when the metal species is copper, Cu (OAc) ₂ , Cu (NO ₃ ) ₂ , CuCl ₂ , Cu (HCOO) ₂ , Cu (CH ₃ COO) ₂ , Cu (CH ₃ CH ₂ COO) ₂ , In addition to CuCO ₃ , CuSO ₄ , and C ₅ H ₇ CuO _2, a basic salt obtained by heating a carboxylate, for example, Cu (OAc) ₂ .CuO can be used in the same manner.
For example, when the metal species is silver, silver nitrate, silver oxide, silver acetate, silver chloride and the like can be used. However, when handled as an aqueous solution, silver nitrate is preferable in terms of its solubility.

  Examples of the method for producing the nanometal particle aqueous dispersion (D) include known and conventional methods such as a method of reducing the metal compound in the presence of the protective agent for nanometal particles in the liquid phase. It can be produced by using the methods described in JP-0337884, JP2008-037949, JP2008-03818, JP2010-007124, and the like.

<Water absorbent resin>
Examples of water-absorbing resins include nonionic water-absorbing resins mainly composed of polyalkylene oxide, resins mainly composed of acrylamide / tertiary butyl sulfonic acid, resins mainly composed of N-vinylcarboxylic acid amide, and the like. It is done.
Cellulose-based products such as cellulose-acrylonitrile graft copolymer and carboxymethylcellulose cross-linked product, polyvinyl alcohol cross-linked products, polyvinyl alcohol-based products such as polyvinyl alcohol water-absorbing gel freeze / thaw elastomer, acrylic acid-sodium / vinyl alcohol co-polymer Polymers, acrylic acid-based products such as sodium polyacrylate crosslinked products, acrylamide-based products such as N-substituted acrylamide crosslinked products, and other polysaccharide-based materials such as hyaluronic acid can also be used.

  Among these, nonionic water-absorbing resins mainly composed of polyalkylene oxide, resins mainly composed of acrylamide / tertiary butyl sulfonic acid, and resins mainly composed of N-vinylcarboxylic amide are preferable. A nonionic water-absorbing resin mainly composed of oxide is more preferable. Further, it is more preferable that the main component polyalkylene oxide is a modified product of polyalkylene oxide. Examples of the modification include urethane modification.

  Examples of the nonionic polyalkylene oxide-based resin include polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymers, or a composite system in which two or more kinds are combined. The polyethylene oxide preferably has a weight average molecular weight of 10,000 to 500,000, and more preferably 20,000 to 100,000. Moreover, as said polypropylene oxide, it is preferable that a weight average molecular weight is 500-50,000, and it is preferable that a weight average molecular weight is 1000-20,000. Furthermore, as a composite system in which any one of ethylene oxide-propylene oxide copolymers or a combination of two or more thereof is used, the weight average molecular weight is preferably 500 to 50,000, and the weight average molecular weight is 1000 to 20,000. It is preferable. If the weight average molecular weight is less than the lower limit, the water absorption tends to be insufficient, and if the weight average molecular weight is exceeded, the moldability and workability tend to decrease.

  Further, the nonionic polyalkylene oxide water-absorbing resin modified product according to the present invention is preferably obtained by crosslinking polyalkylene oxide and polyol with an isocyanate compound. By using the modified nonionic polyalkylene oxide water-absorbent resin thus obtained, water absorption capacity, processability such as molding, shape retention, usability, stability and safety are more excellent. Tend to be.

  As such a polyalkylene oxide, any of the above-mentioned polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, or a composite system in which two or more are combined is preferable.

  The polyol is not particularly limited, but is preferably a low molecular diol having a molecular weight of 500 or less, more preferably ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, triethylene. Methylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, hexylene glycol, octylene glycol, glyceryl monoacetate, glyceryl monobutyrate, 1, Examples thereof include aliphatic or aromatic diols such as 6-hexanediol, 1,9-nonanediol, and 1,4-bishydroxyethylbenzene. Among these, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, and 1,9-nonanediol can be preferably used from the viewpoint of improving water absorption capacity and stability. These low molecular diols can be used alone or in combination of two or more.

  The isocyanate compound is not particularly limited, but is preferably an aliphatic or aromatic diisocyanate, specifically 1,6-hexamethylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,8- Dimethylbenzole-2,4-diisocyanate, 2,4-tolylene diisocyanate, 2,2′-dimethyl-4,4′-diphenylmethane diisocyanate, 1,3- or 1,4-bis (isocyanatomethyl) benzene, 1, 3- or 1,4-bis (isocyanate methyl) cyclohexane, 4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate and the like. Among such aliphatic or aromatic diisocyanates, 1,6-hexamethylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, from the viewpoint of improving water absorption capacity, feeling of use and stability, 4,4′-dicyclohexylmethane diisocyanate and the like can be preferably used. These diisocyanate compounds can be used alone or in combination of two or more.

In the present invention, the polyalkylene oxide and polyol can be cross-linked with an isocyanate compound, generally in the form of a solution using an appropriate solvent such as toluene, xylene or dimethylformamide. However, it is also possible to react in a dispersed state, or after mixing both uniformly in powder or solid form, the reaction can be carried out by heating to a predetermined temperature.
Specific examples include compounds described in formula (I) or (II) of JP-A No. 09-143210.

  As for the usage-amount of a water absorbing resin, it is preferable to use 1-15 parts of water absorbing resin (B) per 100 parts of volatile matter mass conversion in a nano metal particle aqueous dispersion (A).

  Examples of the shape of the water-absorbent resin include pellets and granules. From the viewpoint of efficient redispersion during the refining treatment described later, pellets are preferable.

<Purification treatment>
The water-absorbent resin contains an unavoidable liquid component by simply adding the water-absorbent resin to the nanometal particle aqueous dispersion (D) thus prepared and allowing it to stand for 6 to 24 hours. The liquid can be absorbed. The nanometal covers the periphery of the water-absorbing resin that has absorbed and swollen. By performing these operations in a sealed container, the nanometal can be processed without being completely dried and aggregated.
Thereafter, water or an organic solvent can be added, mixed by hand, filtered on a filter paper, and the nanometal adhering to the water absorbent resin can be dispersed in the filtrate. The nano metal adhering to the water-absorbent resin can be washed away by washing with water or an organic solvent divided into a plurality of times, and can be efficiently dispersed (redispersed) in the filtrate.
Here, the organic solvent may be any organic solvent as long as it does not have an adverse effect such as dissolving the water-absorbent resin. That is, lower alcohols such as ethanol, methanol, propanol and butanol, ketones such as acetone, MEK, MIBK and ethyl acetate, hydrophobic solvents such as toluene and xylene, and high-boiling solvents such as α-terpineol.
<Dehydration process>
The purified nano metal particle aqueous dispersion (D) can be further dehydrated. These can be performed by a known and commonly used method such as a method of adding a solvent to be switched and azeotropically.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these Examples. Unless otherwise specified, “%” represents “mass%”.
<Description of equipment used in the present invention>
[Measurement of nitrate ion concentration]
A portable ion / pH meter, IM-32P type, manufactured by Toa DK Corporation was used. The nanosilver aqueous dispersion was precisely weighed in a container so that the solid content was a predetermined amount, and the nitrate ion concentration extracted by adding a predetermined amount of water to the molten residue after drying at 125 ° C. for 30 minutes was measured.
[Measurement of particle size]
Measurement was performed using a particle size distribution measuring apparatus (Nanotrack (registered trademark), UPA-EX150, manufactured by Nikkiso Co., Ltd.) using a laser Doppler method.

Synthesis Example 1 (Synthesis of nano silver)
(1) <Protective agent and its aqueous solution>
A resin serving as a protective agent was obtained based on Synthesis Example 1 described in Japanese Patent No. 4573138.
To the aqueous solution in which the obtained resin was dissolved (the silver weight was 120 g (the silver weight to be manufactured), the solid content was adjusted to 7.10%. 34.16 g, the concentration was 24.94 wt%). 0.527 wt% hydrogen peroxide was added in the form of a 30% aqueous solution, and the mixture was stirred at room temperature for 1 hour and allowed to stand to obtain an aqueous protective agent solution.
(2) <Silver nitrate aqueous solution>
189.00 g of silver nitrate was added to 314.95 g of water, and stirred and dissolved at room temperature to obtain an aqueous silver nitrate solution. At this time, in order to avoid spontaneous formation of nano silver nuclei by light irradiation, the container used was an aluminum foil wrapped.
(3) <Nanosilver particle aqueous dispersion>
Into a 2,000 mL four-necked flask, 455.63 g of water, 34.31 g of the protective agent aqueous solution obtained in the above (1) and 297.37 g of dimethylaminoethanol were added. The four-necked flask was set in a bath, and nitrogen gas was blown in at 10 mL per minute while stirring with a half-moon blade (250 rpm), and the temperature was raised to 40 ° C. After reaching 40 ° C., the aqueous silver nitrate solution obtained in (2) above was added dropwise over 30 minutes, and then 15.75 g of water in which the container was co-washed was also added dropwise, and then the temperature was raised to 50 ° C. and held for 5 hours. Later, it was allowed to cool naturally.

Example 1 (Purification treatment of the present invention)
In an airtight container, 50 g of the aqueous dispersion of nano silver particles after natural cooling obtained in Synthesis Example 1 (3) was mixed with Aqua Coke TWB (water absorbent resin, urethane-modified polyalkylene oxide) manufactured by Sumitomo Seika Co., Ltd. 5.00 g of Sumitomo Seika Co., Ltd.) was added, and the mixture was stirred for 30 minutes and allowed to stand until the next day. After standing, the liquid was almost absorbed, and it was confirmed that nanosilver covered the swollen water absorbent resin. Since these operations were performed in a closed container, the nanosilver did not dry completely and did not aggregate.
Then, add 50 g of water, mix by hand, filter on filter paper, wash 100 g of water in three portions (first time 25 g water, second time water 25 g, third time water 50 g), water absorption The nano silver adhering to the resin was washed away and dispersed in the filtrate.
<Nitrate ion concentration>
The nitrate ion concentration of the filtrate was measured using an ion electrode. As a result, the nitrate ion concentration decreased to 29% compared to before the purification treatment.
<Particle size>
The particle size of nanosilver in the filtrate was measured with Nanotrac (registered trademark of Nikkiso Co., Ltd.). As a result, no change in particle size was observed before and after the purification treatment.
From this, it can be seen that the inevitable component could be removed and selectively recovered by the method of the present invention without agglomerating or fusing the nano metal particles.

Claims (6)

After the nanometal particle aqueous dispersion (A) containing inorganic acid ions and the water absorbent resin (B) are brought into contact with each other and absorbed, the nanometal particles on the water absorbent resin (B) are mixed with water or an organic solvent. The manufacturing method of the refined nano metal particle aqueous dispersion (D) re-dispersed using. The production method according to claim 1, wherein the aqueous nanometal particle dispersion (A) containing inorganic acid ions is an aqueous nanometal particle dispersion having an inorganic acid ion concentration of 0.001 to 1.5 mol / liter. The production method according to claim 1, wherein the water absorbent resin (B) is a nonionic water absorbent resin containing polyalkylene oxide as a main component. The manufacturing method as described in any one of Claims 1-3 using 1-15 parts water-absorbing resin (B) per 100 parts of mass conversion of the volatile matter in a nano metal particle aqueous dispersion (A). The manufacturing method according to any one of claims 1 to 4, wherein the water absorbent resin (B) is in a pellet form. The purified nanometal particle aqueous dispersion (D) obtained by the production method according to any one of claims 1 to 5, further dehydrated, and the purified nanometal particle solvent dispersion (E). Production method.