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Researchers Submit Patent Application, "Method for Converting Metal with Relative Low Reduction Potential into Metal with Relative High Reduction...

May 22, 2014



Researchers Submit Patent Application, "Method for Converting Metal with Relative Low Reduction Potential into Metal with Relative High Reduction Potential without Changing Its Shape", for Approval

By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors YEH, Chen-Sheng (Tainan City, TW); TSAI, Ming-Fong (Tainan City, TW); CHIEN, Yi-Hsin (Tainan City, TW), filed on June 19, 2013, was made available online on May 8, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a method for converting a metal with relative low reduction potential into another metal with relative high reducing potential and, more particularly, to a method for converting one metal with relative low reduction potential into another metal with relative high reducing potential without changing the shape of the first metal.

"Metal has excellent electric conductivity, ductility and thermal conductivity, and thus is one common material used in various fields. For example, metal is greatly used in circuit designs of semiconductor fields, metal workings, battery productions, and catalyst converting in petrochemical industries. In recent years, metal nano-particles are further applied to catalysts, and biomedical materials for treatment or diagnosis as the development of the nano-technologies. However, some metal materials used in the aforementioned fields are precious metal, such as Au, Pt or Pd, and only a little amount thereof can be obtained on the surface of the earth. Hence, one important issue is to recycle and reuse these metals in wastes.

"Recently, several chemical reactions are known to be used in workings and syntheses of metal materials. One common chemical reaction is galvanic replacement reaction, which is a chemical reaction to convert one metal with relative low reduction potential into another metal with relative high reduction potential.

"However, the shapes of the original reactants cannot be kept after the conventional galvanic replacement reaction is performed. For instance, when Ag in Ag nano-particles is substituted with Au through the known galvanic replacement reaction, the products are hollow Au nano-balls, but not solid Au nano-particles. Hence, it is difficult to maintain the shapes of the original reactants in nano-scale, and further more difficult to maintain the shapes thereof in micro-scale through the known chemical reactions.

"Therefore, it is desirable to provide an improved method, which can convert one metal with relative low reduction potential into another metal with relative high reduction potential without changing its original shape, and be applied to the aforementioned industrial fields."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "An object of the present invention is to provide a method for converting a first metal with relative low reduction potential into a second metal with relative high reducing potential, in which the first metal is replaced by the second metal without changing the original shape of the first metal.

"To achieve the object, the method of the present invention comprises the following steps: providing a first metal substrate and a reaction solution comprising a second metal precursor, a cation surfactant, and a weak reducing agent; and placing the first metal substrate into the reaction solution for a predetermined time to convert the first metal substrate into a second metal substrate, wherein the reduction potential of a first metal of the first metal substrate is lower than that of a second metal of the second metal substrate and the second metal precursor, and shapes of the first metal substrate and the second metal substrate are the same.

"In the conventional galvanic replacement reaction, it is hard to convert a solid reactant object (i.e. the first metal substrate) into a solid product (i.e. the second metal substrate). However, according to the method of the present invention, the rate of removing the first metal and that of filling the second metal can be kept in a balance state by selecting a suitable cation surfactant and a proper weak reducing agent, and therefore the first metal of the first metal substrate can be replaced with the second metal provided by the second metal precursor without changing the original shape of the first metal substrate. Especially, the cation surfactant used in the method of the present invention is one factor for remaining the original shape of the first metal substrate after the reaction is completed.

"In the present invention, the phrases 'without changing the (original) shape' or 'identical (or the same) shape' mean that the shapes of the reactant object and the product are the same, and the sizes thereof are not different substantially. For example, when the reactant object is a solid sphere, the obtained product is also in a form of a solid sphere; and when the reactant object is a metal plate, and the obtained product is also a metal plate. More specifically, a solid reactant object made of a first metal can be converted into a solid product made of a second metal by using the method of the present invention. In the present invention, the forms of the solid reactant object or the solid product may be present in metal nano-particles, nano-wires, metal films, nano-plates, metal foil, nano-rods, nano-spheres, nano-discs, or metal bulks, but the present invention does not limit thereto. The method of the present invention can obtain a product with not only the same shape of the reactant object, but also the similar size thereof by properly adjusting the amount of the second metal precursor.

"In the present invention, the term 'nano-plates' or 'nano-discs' means that the objects have a thickness of 1-100 nm, but the diameter or the width thereof are not particularly limited and can be in micro-scale or in nano-scale. Preferably, the thickness of the nano-plates or the nano-discs is 1-50 nm. More preferably, the thickness thereof is 1-30 nm. However, the present invention is not particularly limited thereto.

"In addition, the term 'nano-wires' or 'nano-rods' means that the objects have a cross-sectional diameter of 1-100 nm, but the length thereof are not particularly limited and can be in micro-scale or in nano-scale. Preferably, the cross-sectional diameter thereof is 1-50 nm. More preferably, the cross-sectional diameter thereof is 1-30 nm. With regard to the length of the nano-rods, it can be 10-100 nm, Preferably, the length thereof is 30-100 nm. However, the present invention is not particularly limited thereto.

"Furthermore, the term 'metal foils' or 'metal films' means that the objects have a thickness of 0.1 .mu.m-1000 .mu.m, but the length, the width or the diameter thereof are not particularly limited. Preferably, the thickness of the metal foils or the metal films is 1 .mu.m-500 .mu.m. However, the present invention is not particularly limited thereto.

"Moreover, the term 'nano-particles' or 'nano-spheres' means that the objects have a diameter of 1-100 nm. Preferably, the diameter of the nano-particles or the nano-spheres is 1-50 nm. More preferably, the diameter thereof is 1-30 nm. However, the present invention is not particularly limited thereto.

"In the method of the present invention, the cation surfactant can be any general cation surfactant used in the art. In one aspect of the present invention, the cation surfactant is represented by the following formula (I):

"##STR00001##

"wherein each R.sub.1, R.sub.2, and R.sub.3 independently is C.sub.1-3 alkyl, R.sub.4 is C.sub.12-22 alkyl, and X.sup.- is a halogen ion.

"In the aforementioned formula (I), specific examples of X.sup.- comprise Cl.sup.-, and Br.sup.-. Preferably, X.sup.- is Br.sup.-. Furthermore, each R.sub.1, R.sub.2, and R.sub.3 may independently be methyl, ethyl, n-propyl, or isopropyl. Preferably, each R.sub.1, R.sub.2, and R.sub.3 independently is methyl or ethyl. More preferably, all R.sub.1, R.sub.2, and R.sub.3 are methyl or ethyl. Most preferably, all R.sub.1, R.sub.2, and R.sub.3 are methyl. In addition, R.sub.4 can be linear or branch C.sub.12-22 alkyl. Preferably, R.sub.4 is linear C.sub.12-22 alkyl. More preferably, R.sub.4 is linear C.sub.14-20 alkyl. Most preferably, R.sub.4 is linear C.sub.15-18 alkyl.

"In the method of the present invention, a specific example of the cation surfactant shown by the formula (I) can be cetyltrimethylammonium bromide (CTAB), but the present invention is not limited thereto. Herein, the concentration of the cation surfactant used in the method of the present invention may be adjusted according to the components (for example, the second metal precursor) contained in the reaction solution or the shape of the first metal substrate, as long as the rate of removing the first metal and that of filling the second metal can be kept in a balance state

"In the method of the present invention, the materials of the first metal substrate, the second metal substrate and the second metal precursor are not particularly limited, as long as the reduction potential of the first metal of the first metal substrate is lower than that of the second metal of the second metal substrate and the second metal precursor. In this case, the purpose of replacing the first metal with the second metal can be achieved. For instance, the first metal of the first metal substrate can be Ag, and the second metal of the second metal substrate or the second metal precursor can be Au, Pd, or Pt. In addition, according to the materials of the first metal substrate and the second metal substrate to be obtained, suitable metal salts can be selected as the second metal precursor contained in the reaction solution. Fore examples, the second metal precursor can be metal salts of Ag, Pd or Pt. In the method of the present invention, specific examples of the second metal precursor comprise H.sub.2PtCl.sub.6, PtS.sub.2O.sub.7H.sub.4, HAuCl.sub.4, H.sub.2PdCl.sub.4, or a combination thereof, but the present invention is not limited thereto.

"In addition, in the method of the present invention, the weak reducing agent in the reaction solution is a reducing agent with reducing capacity lower than that of NaBH.sub.4 or sodium citrate. Herein, a strong reducing agent cannot be selected as the reducing agent used in the reaction solution of the present invention. It is because that the reduction reaction of the second metal precursor is too fast and nano-particles of the second metal may be directly formed in the reaction solution when the reducing capacity of the reducing agent is too strong. In this case, the purpose of replacing the first metal with the second metal cannot be achieved. In the method of the present invention, a specific example of the weak reducing agent is ascorbic acid (AA), i.e. vitamin C; but the present invention is not limited thereto. In addition, a concentration of the weak reducing agent of the present invention can be adjusted according to the shape of the first substrate or each component such as the metal precursor in the reaction solution, as long as the rate of removing the first metal and that of filling the second metal can be kept in a balance state.

"In the method of the present invention, preferably, a molar ratio of the cation surfactant and the weak reducing agent is in a range from 1:1 to 10:1. More preferably, the molar ratio thereof is in a range from 1:1 to 9:1. Most preferably the molar ratio thereof is in a range from 2:1 to 6:1.

"Additionally, in the method of the present invention, preferably, a molar ratio of the second metal precursor and the weak reducing agent is in a range from 1:100 to 1:1. More preferably, the molar ratio thereof is in a range from 1:50 to 1:1. Most preferably, the molar ratio thereof is in a range from 1:10 to 1:2.

"Furthermore, in the method of the present invention, a second metal precursor may be further added into the reaction solution after the replacing reaction is performed for a predetermined time, in the case that the size of the first metal substrate is large.

"Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1A shows TEM photos of nano-discs formed at different reaction times according to Embodiment 1 of the present invention;

"FIG. 1B shows detected UV-visible spectra of nano-discs formed at different reaction times according to Embodiment 1 of the present invention;

"FIGS. 2A-2C are diagrams showing element distributions of nano-discs detected by line-scanning according to Embodiment 1 of the present invention, in which the X axis thereof represents different detection points on the nano-discs;

"FIG. 3A shows TEM photos of nano-discs formed in reaction solutions with different amounts of HAuCL.sub.4 according to Embodiment 2 of the present invention;

"FIG. 3B shows a detected UV-visible spectrum of nano-discs formed in reaction solutions with different amounts of HAuCL.sub.4 according to Embodiment 2 of the present invention;

"FIGS. 4A-4D show TEM photos according to Embodiment 3 of the present invention;

"FIGS. 5A-5C shows TEM photos of nanoprisms formed at different reaction times according to Embodiment 4 of the present invention;

"FIGS. 6A-6C are diagrams showing element distributions of nanoprisms detected by line-scanning according to Embodiment 4 of the present invention, in which the X axis thereof represents different detection points on the nano-prisms;

"FIG. 7 shows detected UV-visible spectra of nanoprisms formed at different reaction times according to Embodiment 4 of the present invention;

"FIGS. 8A-8B are diagrams showing element distributions of metal foils detected by line-scanning according to Embodiment 5 of the present invention, in which the X axis thereof represents different detection points on the metal foils;

"FIGS. 9A-9B shows SEM photos of metal foils according to Embodiment 5 of the present invention, and the magnification thereof is 500.times.; and

"FIGS. 10A-10B shows EDX results of metal foils according to Embodiment 5 of the present invention."

For additional information on this patent application, see: YEH, Chen-Sheng; TSAI, Ming-Fong; CHIEN, Yi-Hsin. Method for Converting Metal with Relative Low Reduction Potential into Metal with Relative High Reduction Potential without Changing Its Shape. Filed June 19, 2013 and posted May 8, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=6785&p=136&f=G&l=50&d=PG01&S1=20140501.PD.&OS=PD/20140501&RS=PD/20140501

Keywords for this news article include: Patents.

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Source: Politics & Government Week


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