Patent Application
20120318678
The present invention relates to an apparatus for producing metal nanoparticles using an electrolysis, and a method thereof, and more particularly, to an apparatus for producing metal nanoparticles using granule type electrodes, in which the metal nanoparticles having a uniform shape and nano-size can be continuously mass-produced in large quantities at low cost by filling granules consisting of the same metal as the metal nanoparticles to be obtained as an electrode material in a pair of electrode housings spaced by a certain interval and electrolyzing the granules with alternating-current (AC) voltage.
In general, chemical methods such as a coprecipitation method, a spraying method, a sol-gel method, an electrolysis method, and a reverse phase micro-emulsion method, and mechanical methods such as a grinding method using a ball mill, or stamp mill, are being used as methods of obtaining fine metal powder.
For example, in the case of the chemical methods of producing silver powder, there are mainly used methods of educing silver powder through a method of reducing a precipitate of silver oxide or silver hydroxide that has been produced through a neutralization reaction process that neutralizes a silver nitrate aqueous solution with an alkaline solution, by use of a reducing agent such as hydrazine, hydrogen peroxide, or formaldehyde often known as formalin, a method of reducing the precipitate of silver hydroxide that has been produced through the neutralization reaction process by inhalation of a gas with a strong reduction force such as hydrogen or carbon monoxide into the precipitate of silver hydroxide, and a method of reducing an alkaline amino complex by addition of a reducing agent such as formaldehyde often known as formalin and oxalic acid into an alkaline amino complex aqueous solution.
However, since these conventional methods use a metallic salt of an electrolyte as a starting material, respectively, they are not environmentally friendly but are costly and time-consuming in order to remove harmful matter, and do not easily control size of particles.
In addition, since the conventional methods use a surfactant, an additive, or harmful matter in order to prevent particle growth due to aggregation of metal particles, they are not environmentally friendly.
In general, the conventional electric decomposition method called electrolysis uses electrodes of a metallic material to be synthesized, and a metallic salt, that is, nitrate, carbonate, or sulfate as an electrolyte, in which the metallic material clings onto the surface of the electrode by the electrolysis, to thereby obtain metallic particles.
The reason why toxic metal salts are being used as electrolytes for obtaining metallic powder in the electrolysis is of course because metal is not soluble in water. Further, if metal combined with a strong acid salt is dissolved in water, it is easily dissociated into metal ions to then be educed into particles by reducing agents.
In this case, harmful matter is produced as a by-product and noxious gases are generated when the temperature increases. Accordingly, the conventional electrolysis is not eco-friendly, nor obtains a uniform size of particles.
Moreover, in the case of the conventional electrolysis using a metallic salt such as nitrate, carbonate, or sulfate, the starting material is not only environmentally friendly in itself, but a waste water treatment problem also occurs during neutralizing and washing processes. Further, a number of washing processes should undergo to thus cause a big burden, and a lot of metal powder is lost in the washing process.
In order to consider and solve the problem that the starting material is not only environmentally friendly in itself, but a waste water treatment problem also occurs in the case of the conventional electrolysis using a metallic salt, a method of producing metal nanoparticles using an electrolysis was proposed in Korean Laid-open Patent Publication No. 10-2004-105914, in which only electrodes, a small quantity of additives, and ultra-pure water (DI-water; DeIonized-water) are used and an external force is applied in the electrolysis, to thus induce formation and dispersion of metal particles, and to thereby produce metal nanoparticles environmentally friendly.
The above-described conventional method of producing metal nanoparticles disclosed in Korean Laid-open Patent Publication No. 10-2004-105914 will be described below in more detail with reference to
As shown in
However, the conventional metal nanoparticles producing method used a direct-current (DC) electrolysis, in which both a positive electrode rod called an anode and a negative electrode called a cathode were made of the same ingredients as those of the metal particles to be obtained in the above-descried Korean Laid-open Patent Publication No. 10-2004-105914. Accordingly, there occurred a phenomenon that metallic crystals were produced on the electrodes by a potential difference between the two electrode rods.
In addition, in the case of producing metal nanoparticles, for example, silver nanoparticles by using the method disclosed in the Korean Laid-open Patent Publication No. 10-2004-105914, metal cations that have been produced at the anode move to the cathode when direct-current (DC) electricity is applied, to then grow to the neighboring portion of the cathode. Accordingly, micro-ordered silver particle crystallines exceeding nano-size are produced, to thereby cause a lumping phenomenon. Further, there have been problems that shape and size of metal particles are not uniform, and non-uniform particles are formed.
In addition, in the case that a DC current is applied across two electrodes to carry out an electrolysis according to the conventional metal nanoparticles producing method, Ag+ ions are combined with OH− ions that are counter ions of the Ag+ ions at the anode, by heat generated when the Ag+ ions are produced, to thus cause a problem of leading to an oxidation phenomenon of the Ag+ ions. The Ag+ ions that are not oxidized move to the cathode by an electric field before the Ag+ ions that are not oxidized are reduced by a reducing agent, and come across electrons provided from the cathode to then be reduced again into silver. As a result, silver particles gradually grow up to a micro-size, to thus cause a result of consuming Ag+ ions to be produced as silver nanoparticles.
Therefore, even if Ag+ ions are reduced by a reducing agent and are capped by a dispersant to thus produce desired nanoparticles, the quantity of the produced nanoparticles that is present in a reaction solution is extremely less than the amount of the oxidized Ag2O and the grown silver nanoparticles. As a result, the conventional metal nanoparticles producing method is not suitable for a highly efficient mass production method.
On the other hand, as a technology of solving the problem that the above conventional metal nanoparticles producing method using the direct-current (DC) electrolysis method is inadequate for the mass production method, a technology of producing metal nanoparticles using an alternating-current (AC) voltage instead of a DC voltage during performing an electrolysis method was proposed in Korean Patent Registration No. 10-0820038.
According to the Korean Patent Registration No. 10-0820038, a copper nanoparticles producing method includes the steps of: putting and melting in water a metal ion reducing agent that is a material capable of reducing hydrazine or copper ions and a metal ion generating agent that is a material capable of ionizing trisodyum citrate or copper on the surfaces of copper electrodes, to thereby obtain a solution; placing the copper electrodes in the solution at a distance from each other, and ionizing the same elements as metal particles to be obtained by the copper electrodes in the solution by an electric energy generated due to an alternating-current (AC) voltage that is applied across the copper electrodes and the metal ion generating agent; and reducing the copper ions in the solution by the reducing agent so that copper particles are educed.
However, according to the Korean Patent Registration No. 10-0820038, pure copper nanoparticles may be obtained, but since a commercial AC voltage of 110V˜220V that is a sine wave of 50˜60 Hz is used, an electrolysis efficiency is very low. The reason is because the AC voltage is applied for the two electrodes and thus polarities of the two electrodes are changed at a constant cycle. That is, since polarities of the two electrodes are changed 50 to 60 times per second in a general commercial AC voltage, metal ions generated at a metal electrode may be reduced but may go back to the metal electrode before reduction, to thereby confront a problem of causing a significant decrease in productivity.
Thus, the average particle size and the distribution of copper particles are not uniform, but a mass productivity is lowered due to crystallization by a change in the polarities of the electrodes.
On the other hand, as shown in
If a gap between the two electrodes is changed as the bar type electrodes are transformed, a potential difference occurs and the amount of electric conduction is decreased, to thus confront a problem of causing an increase in size of metal nanoparticles that are produced by heat generation.
Therefore, in order to maintain a certain interval, the transformed portions are cut at every certain period and then reset or replaced by new electrodes. Accordingly, the electrodes are not used efficiently and effectively, to thereby shorten a lifetime of the electrodes. Moreover, such a resetting process and a replacement process for the electrodes should be periodically done manually, to accordingly confront a problem of causing a decrease in productivity.
To solve the above problems or defects, it is an object of the present invention to provide an apparatus for producing metal nanoparticles using granule type electrodes, in which since electrodes are configured by filling granules or flakes consisting of the same metal material as the metal nanoparticles to be obtained as an electrode material in a pair of electrode housings spaced by a certain interval in an electrolytic chamber, a distance between the electrodes does not change even if an electrolysis proceeds, to thus obtain the metal nanoparticles having a uniform size, and a method thereof.
It is another object of the present invention to provide an apparatus for producing metal nanoparticles in which a large quantity of metal nanoparticles can be produced continuously and conveniently without interruption of production of the metal nanoparticles due to replacement of electrodes by consecutively filling metal granules or flakes that are consumed in an electrolysis process.
It is still another object of the present invention to provide an apparatus for producing metal nanoparticles in which large quantity of metal nanoparticles can be produced at a high efficiency by selecting an optimal frequency from an alternating-current (AC) power supply and then applying the selected optimal frequency to electrodes, in a manner that the metal nanoparticles can be mass-produced by reducing metal ions into the metal nanoparticles by using a reducing agent before the metal ions are crystallized and by changing polarities of the electrodes before the metal ions that are not reduced yet are grown into nano-crystals.
It is yet another object of the present invention to provide an apparatus for producing metal nanoparticles and a method thereof, in which metal nanoparticles can be produced environmentally friendly even by using an alternating-current (AC) electrolysis method.
To accomplish the above and other objects of the present invention, according to an aspect of the present invention, there is provided an apparatus for producing metal nanoparticles, the metal nanoparticles producing apparatus comprising:
a reaction vessel containing an electrolytic solution;
first and second electrodes that are formed by filling a number of granules or flakes consisting of the same metal as the metal nanoparticles to be obtained, in first and second electrode housings that are spaced by a gap in the reaction vessel; and
a power supply that applies an alternating-current (AC) power between the first and second electrodes for electrolysis reaction,
wherein the first and second electrode housings comprise a number of holes or slits on at least two surfaces facing each other so that metal ions dissolved from the first and second electrodes can be discharged depending on the electrolysis reaction.
According to another aspect of the present invention, there is provided an apparatus for producing metal nanoparticles, the metal nanoparticles producing apparatus comprising:
a reaction vessel containing an electrolytic solution;
a first electrode that is formed by filling a number of granules or flakes consisting of the same metal as the metal nanoparticles to be obtained, in an electrode housing that is provided in the reaction vessel;
a second electrode that is spaced by a gap from the first electrode in the reaction vessel; and
a power supply that applies an alternating-current (AC) power between the first and second electrodes for electrolysis reaction,
wherein the electrode housing comprises a number of holes or slits so that metal ions dissolved from the first electrode can be discharged depending on the electrolysis reaction.
Preferably but not necessarily, the metal nanoparticles producing apparatus further comprises a support holder that supports the first and second electrode housings at a distance spaced from each other in an insulation mode.
Preferably but not necessarily, the metal nanoparticles producing apparatus further comprises: first and second power cables that supply the AC power that is applied between the first and second electrodes from a power supply; and first and second electrode terminals that mutually connect granules or flakes that are filled in the inner portions of the first and second electrode housings, respectively on both sides of the support holder.
Preferably but not necessarily, the first and second electrode housings are vessels whose cross-sectional shapes are rectangular or polygonal, respectively.
Preferably but not necessarily, the first and second electrode housings comprise a number of projections whose side surfaces opposing each other are formed in a saw-tooth shape, and first and second side plates having a number of holes or slits formed on both side surfaces of the projections, respectively, and the first and second side plates are formed of a net consisting of Ti.
Preferably but not necessarily, the first and second electrode housings differ from each other in diameter, respectively, and have a structure of circular double vessels that are concentrically disposed. In this case, the metal nanoparticles producing apparatus further comprises an agitator with impellers that are disposed at a distal end of a rotating shaft that is rotatably supported by a bearing that is penetrated and extended through the center of the second electrode housing and supported by a bearing holder.
Preferably but not necessarily, the metal nanoparticles producing apparatus further comprises: conductive plates that are respectively inserted into the internal spaces of the first and second electrode housings to thus contact the granules or flakes.
Preferably but not necessarily, the granules or flakes comprise an alloy made of any one or at least two selected from the group consisting of Ag, Pt, Au, Mg, Al, Zn, Fe, Cu, Ni, and Pd, and the granules or flakes are set in a range of 0.05 to 10 cm in size, and preferably set in a range of 0.5 to 5 mm in size.
Preferably but not necessarily, each of the first and second electrode housings is any one selected from the group consisting of polymer, ceramic, glass, and titanium (Ti).
Preferably but not necessarily, the electrode housing has a cross-shaped accommodation space in the inside thereof, and has a number of holes or slits on the lower side surfaces thereof, and the second electrode is disposed in opposition to the lower side surface of the electrode housing and is formed of a plate shape.
Preferably but not necessarily, the electrode housing has a cross-shaped accommodation space in the inside thereof, and has a number of holes or slits on the side surfaces thereof, and the second electrode accommodates the electrode housing therein and is formed of a cylindrical or cylindrical mesh.
Preferably but not necessarily, the electrode housing is rotationally driven in order to maintain a distance between the first and second electrodes to be constant and the second electrode is made of Ti.
According to still another aspect of the present invention, there is provided a method of producing metal nanoparticles, the metal nanoparticles producing method comprising steps of:
preparing an electrolytic solution by dissolving an electrolyte and a dispersant in pure water in a reaction vessel;
forming first and second electrodes by filling a number of granules or flakes made of the same metal as the metal nanoparticles to be obtained, in first and second electrode housings that are disposed in opposition to each other in the reaction vessel, in which a number of holes or slits are provided on the opposing surfaces;
applying an alternating-current (AC) power between the first and second electrodes for electrolysis reaction, to thus ionize metal granules or flakes into the electrolytic solution to thereby generate metal ions; and
reducing the metal ions by a reducing agent to thus form the metal nanoparticles.
According to yet another aspect of the present invention, there is provided a method of producing metal nanoparticles, the metal nanoparticles producing method comprising steps of:
preparing an electrolytic solution by dissolving an electrolyte and a dispersant in pure water in a reaction vessel;
disposing a first electrode that is formed by filling a number of granules or flakes made of the same metal as the metal nanoparticles to be obtained, in an electrode housing, and a second electrode that is made in a plate or cylindrical shape and opposes at least one surface of the first electrode, in the reaction vessel;
applying an alternating-current (AC) power between the first and second electrodes for electrolysis reaction, to thus ionize metal granules or flakes into the electrolytic solution to thereby generate metal ions; and
reducing the metal ions by a reducing agent to thus form the metal nanoparticles.
Preferably but not necessarily, the reducing agent is put into the electrolytic solution, so that concentration of the reducing agent becomes a certain level in response to concentration of metal ions that are produced as an electrolysis proceeds.
Preferably but not necessarily, the AC power frequency is 0<f<10 Hz in which “f” denotes a frequency, so as to be advantageous in view of yield and particle distribution.
Preferably but not necessarily, the metal nanoparticles producing method further comprising the steps of: periodically detecting consumption of the granules or flakes filled in the first and second electrode housings; and filling new granules or flakes according to the detection result.
As described above, an apparatus for producing metal nanoparticles using granule type electrodes, and a method thereof, according to the present invention, includes electrodes that are configured by filling granules or flakes consisting of the same metal material as the metal nanoparticles to be obtained as an electrode material in a pair of electrode housings spaced by a certain interval in an electrolytic chamber. Accordingly, a distance between the electrodes does not change even if electrolysis proceeds, to thus obtain the metal nanoparticles having a uniform size.
The present invention can produce a large quantity of metal nanoparticles continuously and conveniently without interruption of production of the metal nanoparticles due to replacement of electrodes by consecutively filling metal granules or flakes that are consumed in an electrolysis process.
The present invention can produce a large quantity of metal nanoparticles at a high efficiency by selecting an optimal frequency from an alternating-current (AC) power supply and then applying the selected optimal frequency to electrodes, in a manner that the metal nanoparticles can be mass-produced by reducing metal ions into the metal nanoparticles by using a reducing agent before the metal ions are crystallized and by changing polarities of the electrodes before the metal ions that are not reduced yet are grown into nano-crystals.
The present invention can produce metal nanoparticles environmentally friendly even by using an alternating-current (AC) electrolysis method.
The above and/or other objects and/or advantages of the present invention will become more apparent by the following description. Hereinbelow, a metal nanoparticles producing apparatus and method according to a respective embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Referring to
An agitator 20 that agitates the electrolytic solution 11 is selectively disposed below the first and second electrodes 30 and 40. A heating device 25 for indirectly heating the electrolytic solution 11 is disposed below the reaction vessel 10. A power supply 50 for applying an alternating-current (AC) power to the first and second electrodes 30 and 40 is connected above the reaction vessel 10.
For example, the agitator 20 may employ a structure of rotating a magnet piece 10 arranged in the inside of the reaction vessel 10 by a drive device (not shown) placed in the outside of the reaction vessel 10.
In the first embodiment of the invention, the first electrode 30 and the second electrode 40 use a number of silver (Ag) granules or flakes 30a and 40a, in order to obtain metal nanoparticles to be obtained, for example, silver nanoparticles.
However, the present invention may produce the other kinds of metal nanoparticles in addition to the silver nanoparticles using silver (Ag) granules or flakes 30a and 40a. In other words, the present invention may use any material that can elute metal ions of copper (Cu), nickel (Ni), gold (Au), palladium (Pd), and platinum (Pt) in addition to silver (Ag), in the form of granules or flakes, in the first electrode 30 and the second electrode 40.
In this case, the first electrode 30 and the second electrode 40 are formed by filling a number of granules or flakes (hereinbelow, referred to as simply granules) 30a and 40a, into first and second rectangular electrode housings 32 and 42, respectively. However, the first and second electrode housings 32 and 42 are not limited to their shapes if the electrode housings contain granules therein and contact areas of the first and second electrodes 30 and 40 with respect to the electrolytic solution 11 are large.
The granules 30a and 40a used in the second electrode 40 and the first electrode 30 may use the same material as the metal nanoparticles (or metal particles) to be produced. If the first and second electrode housings 32 and 42 have a structure of including a number of slits, holes or nets, it is preferable that granules 30a and 40a are about 0.05 to about 10 cm in size. More preferably, granules 30a and 40a are about 0.5 to about 5 mm in size.
In addition, the first and second electrode housings 32 and 42 that are respectively filled with granules 30a and 40a that are used as the first electrode 30 and the second electrode 40 are maintained at a certain interval by the support holder 15. In other words, a pair of rectangular throughholes are formed on the support holder 15, in correspondence to the cross-sectional shapes of the first and second electrode housings 32 and 42. In the case that the first and second electrode housings 32 and 42 are coupled with the throughholes of the support holder 15, the support holder 15 supports the upper sides of the first and second electrode housings 32 and 42 in an insulation mode, to thus maintain a certain gap between the first and second electrode housings 32 and 42. The remaining portions of the first and second electrode housings 32 and 42 are exposed to the lower side of the support holder 15, while facing each other at a certain interval.
Meanwhile, a number of slits or holes (hereinafter simply referred to as slits) 33 and 43 are respectively formed on the opposing surfaces or side surfaces of the first and second electrode housings 32 and 42. The slits 33 and 43 may use any shapes of sizes and structures capable of accommodating the electrolytic solution 11 in the first and second electrode housings 32 and 42 and eluting the electrolyzed metal nanoparticles.
The granules 30a and 40a are consumed as the electrolysis reaction proceeds. In this case, the granules 30a and 40a are filled consecutively into the first and second electrode housings 32 and 42. As a result, the electrodes do not need to be replaced. The slits 33 and 43 may be formed obliquely upwards on the outer surfaces of the first and second electrode housings 32 and 42 as it goes to the outside of the first and second electrode housings 32 and 42, with a structure that the granules 30a and 40a may not escape. Here, the slits 33 and 43 are set to have the widths smaller than the sizes of the granules 30a and 40a, preferably are set to have about 0.1 to about 1 mm.
Here, a substance used in the first and second electrode housings 32 and 42 may be an insoluble material for the electrolytic solution 11, preferably a dielectric material, for example, polymer family such as MC nylon, nylon, polyester, polystyrene, and polyvinyl chloride, carbon, ceramic or glass, for example, such as Pyrex glass, or titanium (Ti) insoluble for the electrolytic solution 11 but through which current flows.
However, the first and second electrode housings 32 and 42 may employ any shapes or materials if a number of slits, holes, grids or nets through which metal, for example, silver (Ag) ions can pass are formed on the opposing surfaces or side surfaces of the first and second electrode housings 32 and 42.
In addition, the first and second electrode housings 32 and 42 may be configured to have the opposing surfaces made of titanium (Ti), side plates having a number of slits, holes, grids or nets, and the remaining portions made of the polymer family, ceramic or glass to then be assembled with one another.
Furthermore, the first and second electrode housings 32 and 42 may use sacks formed of woven fabric or non-woven fabric that is made of an insoluble material in the electrolytic solution in the case of the material or shape through which metal ions can pass. When woven fabric or non-woven fabric is used as the electrode housing, the first electrode 30 and the second electrode 40 may use powder of a particle diameter of about 1 cm to about 0.5 μm instead of the granules.
For example, first and second bolt-shaped electrode terminals 34 and 44 are respectively fixed on both sides of the support holder 15. An alternating-current (AC) voltage is applied to the granules 30a and 40a contained in the first and second electrode housings 32 and 42 via the first and second bolt-shaped electrode terminals 34 and 44. The first and second bolt-shaped electrode terminals 34 and 44 are connected to the power supply 50 via a pair of power cables 55 that are connected by first and second lugs 35 and 45 for protecting the electrode terminals, to thus receive the AC voltage. In this case, the support holder 15, the first and second electrode terminals 34 and 44 and the pair of the power cables 55 are preferably exposed to the outside of the reaction vessel 10, to thus be prevented from contacting the electrolytic solution 11.
The power supply 50 is connected to the pair of the power cables 55 that are exposed to the outside of the reaction vessel 10, to thus apply the AC power required for electrolysis from the outside of the reaction vessel 10 to the inside thereof. The power supply 50 includes, for example, a function generator for allowing for selection of waveform and frequency of the AC power needed for electrolysis, and an amplifier for amplifying current or voltage of the AC power generated from the function generator. The output of the amplifier is connected to the first electrode 30 and the second electrode 40, respectively.
However, in the case of a mass production line, the power supply 50 that is used in the present invention may employ any type of a power supply such as a dedicated power supply for supplying AC power in which current or voltage having predetermined waveform and frequency and a desired size may be set in advance for the first and second electrodes 30 and 40. In addition, a constant current source may be provided for a power supply so that a preset constant intensity of current may be applied between the first and second electrodes 30 and 40 during performing an electrolysis method in the present invention.
The waveform of the AC power may employ, for example, any waveform such as a sine wave, square wave, triangle wave, sawtooth wave, or the like. Changes in the waveform of the AC power may only cause somewhat a difference in a yield of metal nanoparticles and a particle shape thereof.
Meanwhile, in order to investigate an effect of frequency as a factor affecting a yield in the production of metal nanoparticles by an electrolysis method in the present invention, a yield, particle size distribution and growth of the obtained metal nanoparticles were examined while varying frequency of AC power from 0.1 Hz to 100 Hz.
As a result, it is preferable that frequency “f” of AC power is 0<f<10 Hz, in view of a yield of nanoparticles, especially it is more preferable that the frequency “f” is 0.1≦f≦5 Hz. In addition, when considering the yield, particle size distribution and particle growth, it is the most preferable that the frequency “f” is 0.1≦f≦1 Hz.
If a frequency of supplied power is 0 Hz, namely, the supplied power is direct-current (DC) power, there are one problem that metal ions may be oxidized at the anode, and the other problem that the metal ions that are not oxidized move to the cathode by an electric field before the metal ions that are not oxidized are reduced by a reducing agent, and come across electrons provided from the cathode to then be reduced again into the metal on the surface of the cathode, with a result that the metal particles gradually grow up to a micrometer scale in size, to thus cause a result of lowering a yield of desired metal nanoparticles.
In addition, if the frequency “f” of the AC power exceeds 10 Hz, there is a problem that a yield tends to decrease rapidly, and the grown particles are also found somewhat.
In the case of changing the frequency of AC power from 100 Hz to 0.1 Hz, distribution and the particle sizes of metal nanoparticles have decreased as the frequency decreases from 100 Hz to 10 Hz. Especially, when the frequency of AC power is changed from 10 Hz to 0.1 Hz, distribution and the particle sizes of metal nanoparticles have also further decreased.
The reason why such a phenomenon occurs is because polarities of both electrodes are changed faster and faster as the frequency of AC power is changed from a low frequency to a high frequency, and accordingly produced metal ions are again drawn to an electrode that has been changed into a negative (−) polarity before being participated in a reduction reaction, so as to be plated on the surface of the electrode that has been changed into a negative (−) polarity. In other words, since the positive (+) polarity electrode is changed into the negative (−) polarity electrode before the metal ions produced from the positive (+) polarity electrode momentarily react with the reducing agent to then be reduced into metal nanoparticles, the produced metal ions return to the electrode that produced the metal ions.
In contrast, since a phenomenon that the produced metal ions return to the electrode that produced the metal ions is significantly reduced as the frequency of AC power is decreasingly changed from a high frequency to a low frequency, a phenomenon of increasing a yield of producing nanoparticles appears.
Hereinbelow, in the case of producing metal nanoparticles by an electrolysis method according to the present invention, requirements for producing metal nanoparticles of narrow particle size distribution (i.e., uniform grain) of a uniform shape and a desired size (less than 100 nm) as well as in a high yield will be examined.
In general, in the case of producing metal nanoparticles by an electrolysis method, a method of consecutively producing metal ions from a metal electrode according to time and performing a reduction reaction of the produced metal ions with a reducing agent is employed, instead of a method of determining the quantity of metal particles to be obtained as in chemical methods and then putting the quantity of metal ions that are appropriate for an initial reaction condition into a reaction vessel so that a metal nanoparticles producing reaction proceeds. As a result, the produced metal nanoparticles may return again to the metal electrode that produced the metal ions due to an interaction between the polarity of the electrode and the nanoparticles in the course of the reaction. However, such a phenomenon may cause the biggest problem of lowering a yield, that is, mass-production.
In order to solve the above-described problem of lowering the mass-production in the case of producing metal nanoparticles by an electrolysis method, it is required that concentration of a reducing agent for reducing the metal ions should be maintained adequately according to concentration of metal ions that are produced by applied electric energy.
In this case, the quantity of metal ions to be produced is determined by strength of the current of the AC power that is applied between two electrodes. The strength of the current may be controlled by concentration of an electrolyte and a voltage that is applied across the electrodes. According to further studies conducted by the present inventors, when concentration of the reducing agent is maintained at a constant level considering concentration of metal ions that are produced by intensity of a constant current (i.e., a current value), it have found that a yield of the metal nanoparticles is higher.
The reason is because the amount of the reducing agent is relatively poor if the more quantity of metal ions are produced in comparison with the concentration of the reducing agent, to thus relatively reduce a reduction rate of the metal ions but cause no problems of affecting the yield greatly. However, if the amount of the reducing agent is relatively poor, a side effect of growing the particle size is inevitable. Meanwhile, if concentration of the reducing agent is extremely larger than concentration of metal ions that are produced, the reduction rate of the metal ions becomes too fast. Therefore, the quantity of particles not more than several nanometers are produced and go back to the electrode again even before the particles are capped by a dispersant, to thereby cause a yield to be decreased sharply.
On the other hand, type and concentration of an electrolyte are involved directly with pH of the electrolyte and strength of current applied to the electrolyte. Typically, the electrolyte is usually classified into an acidic electrolyte, a basic electrolyte, and a neutral electrolyte. If only an acidic electrolyte is used, the pH of the electrolyte is smaller than 7. For example, if hydrazine that is weak alkaline is put as a reducing agent, the hydrazine undergoes an acid-base reaction with respect to the acidic electrolyte. Thus, only in the case that a sufficient amount of hydrazine is put, a reduction rate in the reaction is controlled to thus adjust the particle size.
Meanwhile, when only a basic electrolyte is put, the pH of a reaction solution is not less than 7. A chance that electrons may move in the reaction solution increases, and a reaction rate of hydrazine that is weak alkaline and that is used as a reducing agent increases, to thus produce particles of several nanometers. As a result, there occurs a phenomenon that the produced particles return to the electrode that produced the particles before being protected by a dispersant.
Considering this point in the present invention, acidic and basic electrolyte mixture is used, and thus pH is set at 7 to 9.
In addition, relationship between the pH of the reaction solution and the concentration of the reducing agent will be examined below. If pH is less than 7, the reaction rate of hydrazine that is the reducing agent is reduced. The reason is because hydrazine is weak alkaline to thus react with citric acid that is an electrolyte, and thus participates in an acid-base reaction rather than a reduction reaction until pH becomes neutral. This causes a reduction capability of hydrazine to be decreased. Thus, since the reduction reaction takes place after the acid-base reaction takes place, the amount of hydrazine that participates in the reduction reaction with the metal ions is less than the amount of hydrazine that is actually added in the reaction vessel, to thus result in a delay in the reduction reaction so as to increase sizes of the metal particles. In other words, the amount of the reducing agent that has been put in the reaction vessel is less than a desirable range, to thus cause no big problem in the yield, but cause a phenomenon of increasing sizes of particles to be larger than several hundred nanometers.
If a dispersant having a dispersing capability is essentially used and concentration of a reducing agent is maintained to be a certain level in proportion to concentration of metal ions that are produced between pH 7 and pH 9, a reduction rate is maintained relatively at a constant rate, to thus greatly increase a yield (that is, mass productivity).
The method for producing metal nanoparticles using an electrolysis method according to the present invention, can be implemented by a metal nanoparticles production apparatus, and includes the steps of: preparing an electrolytic solution 11 by dissolving a dispersant and an electrolyte in ultra-pure water (DI-water) in a reaction vessel 10; disposing first and second electrodes 30 and 40 made of the same metal as the metal nanoparticles to be obtained, at a distance spaced from each other, in the electrolytic solution 11; ionizing metals of the first and second electrodes 30 and 40 into the electrolytic solution 11 according to the electrolysis method in which an alternating-current (AC) power having a predetermined frequency “f” is between the first and second electrodes 30 and 40; and reducing the metal ions by a reducing agent to thus form the metal nanoparticles.
First of all, in the present invention, the electrolytic solution 11 includes pure water, especially preferably ultra-pure water including an electrolyte, a reducing agent, and a dispersant as additives.
The electrolytic solution 11 is a mixture of acidic and alkaline electrolytes, and is preferably set to be pH 7 to pH 9. In this case, the electrolyte may be a mixture of citric acid and hydrazine.
The electrolyte can be selected from nitric acid, formic acid, acetic acid, citric acid, tataric acid, glutaric acid, hexanoic acid, alkali metal salts of the acids, ammonia (NH3), triethyl amine (TEA), and pyridine amine.
In particular, citric acid that is an environmentally friendly electrolyte may be used as an electrolyte in the present invention and amino acid such as glycine may be used as necessary.
In addition, the reducing agent may be any one or at least two selected from the group consisting of hydrazine (N2H4), sodium hypophosphite (NaH2PO2), sodium borohydride (NaBH4), dimethylamine borane (DMAB: (CH3)2NHBH3), formaldehyde (HCHO), and ascorbic acid.
For example, the reducing agent is an eco-friendly reducing agent, and thus it is preferable to use an organic ion reducing agent such as hydrazine.
The organic ion reducing agent produces nitrogen gas and water in the reaction and is completely consumed, and thus is not harmful after completion of the reaction.
The reducing agent is put into the electrolytic solution through a reducing agent supply device (not shown), in a manner that concentration of the reducing agent becomes a certain level in response to concentration of metal ions that are produced when an electrolysis reaction proceeds depending on an application of the AC power.
As described above, the present invention does not use the electrolyte that is harmful to the environment based on pure water or ultra-pure water (DI-water), but uses the environmentally friendly electrolyte and the eco-friendly organic ion reducing agent, thereby obtaining the metal nanoparticles via an eco-friendly simple way.
Meanwhile, the dispersant plays a role of capping surfaces of metal nanoparticles so that metal ions are dissociated and ionized from the first and second electrodes 30 and 40 according to the electrolysis are reduced by the reducing agent, to then prevent the reduced metal nanoparticles from going back to the electrode to be attached on the electrode or settling due to cohesion between the metal nanoparticles. A water-soluble polymer dispersant or a water dispersible polymer dispersant may be used as the dispersant.
The water-soluble polymer dispersant may be an aqueous polymer dispersant of polyacrylate, polyurethane, or polysiloxane group, and the water dispersible polymer dispersant may be an aqueous polymer dispersant of polyacrylate, polyurethane, or polysiloxane group.
The commercial dispersant that is used as the dispersant may be one or at least two selected from the group consisting of Disperbyk™-111, Byk™-154, Disperbyk™-180, Disperbyk™-182, Disperbyk™-190, Disperbyk™-192, Disperbyk™-193, Disperbyk™-2012, Disperbyk™-2015, Disperbyk™-2090, and Disperbyk™-2091 of BYK Chemie; Tego™ 715w, Tego™ 735w, Tego™ 740w, Tego™ 745w, Tego™ 750w, Tego™ 755w, and Tego™ 775w of Evonik; Solsperse™ 20000, Solsperse™ 43000, and Solsperse™ 44000 of Lubrizol; EFKA™ 4585 of Ciba; Orotan™ 731A, and Orotan™ 1124 of Dow; Tween 20 and Tween 80 of Aldrich; polyethylene glycol (PEG) 200, polyvinylpyrrolidone (PVP) 10,000, PVP 55,000, Poloxamer 407, and Poloxamer 188.
The ultra-pure water (DI-water) refers to tertiary distilled water with little or no anions and cations that are commonly present in tap water or bottled water. The reason of using the ultra-pure water (DI-water) is because impurities may be produced in addition to desired metal nanoparticles, and complex compounds may be also produced, to thereby fail to obtain the metal nanoparticles, when anions and cations are added other than the electrolyte and the reducing agent in the course of producing the metal nanoparticles.
As shown in
Thereafter, citric acid of 2.0 mmol as the electrolyte and hydrazine of 6.0 mmol as the electrolyte were put into ultrapure water (DI-water) of 1 L, and then the ultrapure water (DI-water) of 1 L mixed with the citric acid of 2.0 mmol and the hydrazine of 6.0 mmol are put into the reaction vessel, together with the dispersant of 8.0 g such as BYK Chemie's Disperbyk™-190, and stirred by using the agitator 20 until the citric acid, the hydrazine and the dispersant were completely dissolved.
The aqueous solution in which all additives had been dissolved was heated up to the solution temperature of 90° C. and then a steady stream of coolant was made to flow into the reaction vessel to maintain a preset temperature. At the state of maintaining the preset temperature, a sinusoidal AC power of frequency of 1 Hz was applied between the first and second electrodes while a current value was set to 4.3 A to thus carry out an electrolysis reaction. In addition, while conducting electrolysis for 1 hour 30 minutes, hydrazine of 18.0 mmol was injected as the reducing agent by a constant injection operation using a pump, to thereby conduct the reaction.
After the electrolysis reaction, consumption of the silver electrodes was measured. As a result of analyzing the silver nanoparticles present in the aqueous solution by FE-SEM (Field Effect-Scanning Electron Microscopy), it could be seen that the obtained the silver nanoparticles were in the range of 12 nm to 20 nm in size, and confirmed that very narrow particle distribution was made.
As described above, in the case of producing the metal nanoparticles according to the first embodiment of the present invention, by using the electrolysis method, the silver nanoparticles having a small, uniform size and uniform shape in size of tens of nanometers, could be obtained.
In addition, the present invention is configured to have a pair of electrodes that are formed by filling granules into a pair of electrode housings and that maintain a certain distance spaced from each other, in which the electrodes are changed in the form of granules instead of a metal plate or rod. Then, an electrolysis process is carried out by AC power. Even if the electrolysis process is carried out, a distance between the two electrodes does not change, to thus mass-produce metal nanoparticles of a uniform shape and uniform nano-size.
In addition, since the granules filled in the pair of the electrode housings are consumed when the electrolysis proceeds in the present invention, new granules are filled in the electrode housings, thereby continuously mass-producing metal nanoparticles without interrupting the electrolysis process. As a result, the present invention can increase productivity of producing metal nanoparticles without interrupting the electrolysis process by supplementing metal grains of a granule shape into the inner spaces of the electrode housings instead of replacing the electrodes that are consumed in the electrolysis process.
Referring to
Thus, the same reference numerals are given to the same components as those of the first embodiment of the invention, and thus a detailed description thereof will be omitted.
The holes 33a and 43a in the second embodiment of the present invention may be formed obliquely upwards on the outer surfaces of the first and second electrode housings 32 and 42 as it goes to the outside of the first and second electrode housings 32 and 42, with a structure that the granules 30a and 40a may not escape.
Referring to
As described above, in the case that the conductive plates 37 are respectively inserted in the inside of the first and second electrode housings 32 and 42, the electrical conductivity can be further improved to increase an electrolysis efficiency.
Here, in
In the metal nanoparticles producing apparatus according to the third embodiment of the present invention, the same reference numerals are given to the same components as those of the first embodiment of the invention, and thus a detailed description thereof will be omitted.
Referring to
According to the third embodiment of the present invention, the first and second cylindrical electrode housings 62 and 72 are configured to have a double vessel structure whose bottom is stuck so as to provide annular accommodation spaces into which a number of granules 60a and 70a can be filled, respectively.
According to the third embodiment of the present invention, the first electrode 60 and the second electrode 70 that are filled with the number of the granules 60a and 70a made of the same materials as those of the metal nanoparticles to be obtained, are used in the inside of the first and second cylindrical electrode housings 62 and 72 having a double vessel structure that have different diameters from each other and that are concentrically disposed in a reaction vessel 10.
The first electrode 60 and the second electrode 70 are connected to each other by a number of connection portions 12 of an identical length between the first electrode housing 62 and the second electrode housing 72, and thus are disposed at a distance spaced apart from each other. As a result, the distance between the first electrode housing 62 and the second electrode housing 72 is set to be constant on all the opposing outer circumferences of the first electrode housing 62 and the second electrode housing 72, and thus a distance between the first electrode 60 and the second electrode 70 is set to be constant.
In addition, a number of slits or holes 63 are formed on the inner circumference of the first electrode housing 62, and a number of slits or holes 73 are formed on the outer circumference of the second electrode housing 72 opposing the first electrode housing 62.
Meanwhile, according to the third embodiment, in order to agitate the electrolytic solution 11 contained in the reaction vessel 10, an impeller, i.e., an agitator 20 is placed below the first electrode 60 and the second electrode 70. A rotating shaft 22 of the agitator 20 is disposed to pass through the center of the second electrode housing 72. One end of the rotating shaft 22 is rotatably supported by a bearing 14 that is supported by a number of connection portions 13 in the inside of the lower portion of the second electrode housing 72.
The electrolytic solution 11 that is formed by mixing pure water, preferably ultra-pure water with an electrolyte, a reducing agent, and a dispersant as additives, is accommodated in the inside of the reaction vessel 10. A heating device (not shown) for indirectly heating the electrolytic solution 11 is disposed below the reaction vessel 10. A power supply 50 for applying an alternating-current (AC) power across the first electrode 60 and the second electrode 70 is connected above the reaction vessel 10 through a pair of power cables 55.
The metal nanoparticles producing apparatus having the above-described structure according to the third embodiment of the present invention, employs the first and second cylindrical electrode housings 62 and 72 of the double vessel structure, in order to maximize an opposing area between the first electrode 60 and the second electrode 70, to thus increase the opposing area and to thereby increase the yield of the metal nanoparticles.
In addition, in the case of the third embodiment of the present invention, the first and second electrodes 60 and 70 are configured by filling the granules into the first and second electrode housings 62 and 72 and maintaining a certain distance between the first and second electrodes 60 and 70, in which the electrode material is used in the form of granules instead of a metal plate or rod. Thus, even if an electrolysis process is carried out by using AC power, a distance between the first and second electrodes 60 and 70 is not changed, to thus mass-produce metal nanoparticles of a uniform shape and uniform nano-size.
In addition, according to the present invention, if the granules 60a and 70a filled in the first and second electrode housings 62 and 72 are consumed depending on the electrolysis process, new granules 60a and 70a are filled in the first and second electrode housings 62 and 72. Accordingly, a large quantity of metal nanoparticles can be produced continuously without stopping the electrolysis process. As a result, the present invention can prevent interruption of the electrolysis process and can increase productivity by a continuous process by filling granule shaped metal grains in the inner spaces of the electrode housings without the need to replace the electrodes that are consumed in the electrolysis process.
Referring to
According to the fourth and fifth embodiments of the present invention, a first electrode 80 or 80a is formed of granules accommodated in the electrode housing 82 or 82a, and a second electrode 90 or 90a facing the first electrode 80 or 80a is formed of a disc-shaped circular plate or a cylinder-shaped cylindrical vessel that is energized when AC power is turned on for an electrolysis. The electrode housing 82 or 82a containing granules are rotated by a rotary drive device (not shown).
The second electrode 90 or 90a according to the fourth and fifth embodiments of the present invention is made of a metallic material such as titanium (Ti) that is not dissolved in an electrolytic solution.
In the metal nanoparticles producing apparatus shown in
In this case, since the disc-shaped second electrode 90 is disposed below the first electrode 80, slits 83 of the electrode housing 82 are disposed at the bottom of the electrode housing 82 in order to discharge the metal ions dissolved at the time of electrolysis.
Since the lower plate 84 of the electrode housing 82 and the second disc-shaped electrode 90 are placed at a distance spaced from each other, a certain gap is also persistently maintained between the first and second electrodes 80 and 90.
In addition, since the electrode housing 82 is made to rotate, it is unnecessary to use a separate agitator, to thus expect to promote leaching of metal ions discharged from the first electrode 80.
When the electrode housing 82 is rotated, a constant gap is continuously maintained between the first and second electrodes 80 and 90 and an effective reaction environment is formed between the produced metal ions and the reducing agent at the time of the electrolysis reaction, to thus maximize a mixing efficiency.
In
In the metal nanoparticles producing apparatus shown in
The fifth embodiment of the present invention differs from the fourth embodiment of the present invention, in a point that a second electrode 90a facing a first electrode 80a is formed of a cylinder of a cylindrical or mesh structure having a uniform thickness while surrounding an electrode housing 82a of the first electrode 80a.
In this case, since the cylinder-shaped second electrode 90a is disposed at the lateral sides of the first electrode 80a, slits 83a of the electrode housing 82a are disposed at the lateral side surfaces of the electrode housing 82a in order to discharge the metal ions dissolved at the time of electrolysis.
In the case of the electrode housing 82a is formed of a cross shape, four side surfaces 84a and the cylinder-shaped second electrode 90a are placed at regular intervals. Accordingly, a certain gap is also persistently maintained between the first and second electrodes 80a and 90a.
In addition, since the electrode housing 82a is made to rotate, it is unnecessary to use a separate agitator, to thus expect to promote leaching of metal ions discharged from the first electrode 80a.
Only one electrode housing 82 or 82a is respectively used in the fourth and fifth embodiments of the present invention, it is advantageous to make it easy to supplement granules to be consumed.
In a first electrode 300a and a second electrode 400a shown in
The metal nanoparticles producing apparatus according to the sixth embodiment of the present invention, provides an electrode structure of maximizing an edge effect that ions leached from an electrode are more greatly produced at the edges of the electrode than the other portions of the electrode except for the edges thereof during performing an electrolysis.
To this end, in the metal nanoparticles producing apparatus according to the sixth embodiment of the present invention, first and second electrode housings 32a and 42a formed of for example a rectangular shaped vessel to accommodate granules (not shown) include first and second side plates 34a and 44a whose opposing side surfaces are made of an insoluble electrode material such as Ti, and from which a plurality of serrated projections 35a and 45a (corresponding to threads) protrude at a certain height, respectively.
In this case, the first and second electrode housings 32a and 42a according to the sixth embodiment of the present invention, may use the same material as the insoluble insulation material used in the electrode housings according to the first to third embodiments of the present invention, for example, a polymer family such as MC nylon, nylon, polyester, polystyrene, and polyvinyl chloride, ceramic or glass, for example, pyrex glass. An insoluble material for example such as titanium (Ti) through which an electric current may flow may be used for the first and second side plates 34a and 44a.
As a result, in the case that titanium (Ti) is used for the first and second side plates 34a and 44a of the first and second electrode housings 32a and 42a, and since the first and second side plates 34a and 44a contact a number of granules filled in the first and second electrode housings 32a and 42a, the first and second side plates 34a and 44a are electrically conducted with the number of granules upon an application of AC power to the granules.
In the case of the first and second side plates 34a and 44a as illustrated in
In addition, since the first and second side plates 34a and 44a have a structure that a plurality of serrated projections 35a and 45a (corresponding to threads) protrude at a constant height, respectively, an opposing surface area is increased when compared with a flat plate structure, to thereby enhance an efficiency of obtaining metal nanoparticles by an electrolysis process.
Thus, when AC power is applied to the granules, the opposing projections 35a and 45a of the first and second side plates 34a and 44a are electrically connected with the number of the granules. In this case, the number of the granules that are filled at one side of the first and second electrode housings 32a and 42a thereby forming the first electrode 300a emit electrons to the number of the granules of the second electrode 400a of the other side thereof, to thus increase leaching of metal ions that are leached into the electrolytic solution.
In addition, in the case of the metal nanoparticles producing apparatus according to the sixth embodiment of the present invention as illustrated in
Furthermore, in the first and second electrode housings 32a and 42a in accordance with the sixth embodiment of the present invention, the projections 35a and 45a of the first and second side plates 34a and 44a are arranged in parallel with each other in the vertical direction, but may be arranged in parallel with each other in the horizontal direction.
As described above, the present invention includes electrodes that are configured by filling granules or flakes consisting of the same metal material as the metal nanoparticles to be obtained as an electrode material in a pair of electrode housings spaced by a certain interval in an electrolytic chamber. Accordingly, a distance between two electrodes does not change even if an electrolysis proceeds, to thus obtain the metal nanoparticles having a uniform size.
The present invention can produce a large quantity of metal nanoparticles continuously and conveniently without interruption of production of the metal nanoparticles due to replacement of electrodes by consecutively filling metal granules or flakes that are consumed in an electrolysis process. As a result, the present invention can prevent interruption of the electrolysis process and can increase productivity by a continuous process by filling granules in the electrode housings without the need to replace the electrodes that are consumed in the electrolysis process.
The present invention can produce a large quantity of metal nanoparticles at a high efficiency by selecting an optimal frequency from an alternating-current (AC) power supply and then applying the selected optimal frequency to electrodes, in a manner that the metal nanoparticles can be mass-produced by reducing metal ions into the metal nanoparticles by using a reducing agent before the metal ions are crystallized and by changing polarities of the electrodes before the metal ions that are not reduced yet are grown into nano-crystals.
A case that silver (Ag), for example, having small ionicity is used as a material of granules or flakes has been described in the embodiments, but a metal having large ionicity for example such as Mg, Al, Zn, Fe, and Cu, as well as even a metal having small ionicity for example such as Pt and Au may be used as a material of granules or flakes, to thereby obtain a similar result.
In addition, a case that pure silver (Ag) is used as a material of granules or flakes has been described in the embodiments, but an alloy of two or more metals selected from the group consisting of Ag, Pt, Au, Mg, Al, Zn, Fe, Cu, Ni, and Pd, for example such as Ag—Cu, Ag—Mg, Ag—Al, Ag—Ni, Ag—Fe, Cu—Mg, Cu—Fe, Cu—Al, Cu—Zn, and Cu—Ni alloys may be used as a material of granules or flakes, to thereby obtain alloy nanoparticles.
Furthermore, since all alloy nanoparticles have a melting point lower than that of each pure metal, respectively, a low sintering temperature may be expected when manufacturing ink by using the alloy nanoparticles.
As described above, the present invention has been described with respect to particularly preferred embodiments. However, the present invention is not limited to the above embodiments, and it is possible for one who has an ordinary skill in the art to make various modifications and variations, without departing off the spirit of the present invention. Thus, the protective scope of the present invention is not defined within the detailed description thereof but is defined by the claims to be described later and the technical spirit of the present invention.
The present invention may be widely used for manufacturing metal nanoparticles that are used for applications such as metallic ink, medicine, clothing, cosmetics, catalysts, electrode materials, and electronic materials, particularly for uniformly mass-producing silver nanoparticles in a simple process and eco-friendly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2010-0017692 | Feb 2010 | KR | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/KR2011/001332 | Feb 2011 | US |
| Child | 13592684 | US |
