US20140116573A1 - Method for converting metal with relative low reduction potential into metal with relative high reduction potential without changing its shape - Google Patents

Method for converting metal with relative low reduction potential into metal with relative high reduction potential without changing its shape Download PDF

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US20140116573A1
US20140116573A1 US13/921,740 US201313921740A US2014116573A1 US 20140116573 A1 US20140116573 A1 US 20140116573A1 US 201313921740 A US201313921740 A US 201313921740A US 2014116573 A1 US2014116573 A1 US 2014116573A1
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metal
metal substrate
nano
reduction potential
present
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Chen-Sheng Yeh
Ming-Fong Tsai
Yi-Hsin CHIEN
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National Cheng Kung University NCKU
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National Cheng Kung University NCKU
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/018—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of a noble metal or a noble metal alloy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0551—Flake form nanoparticles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0553—Complex form nanoparticles, e.g. prism, pyramid, octahedron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C5/00—Alloys based on noble metals
    • C22C5/02—Alloys based on gold
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C5/00—Alloys based on noble metals
    • C22C5/06—Alloys based on silver
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape

Definitions

  • 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.
  • metal is greatly used in circuit designs of semiconductor fields, metal workings, battery productions, and catalyst converting in petrochemical industries.
  • metal nano-particles are further applied to catalysts, and biomedical materials for treatment or diagnosis as the development of the nano-technologies.
  • 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.
  • 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.
  • the shapes of the original reactants cannot be kept after the conventional galvanic replacement reaction is performed.
  • the products are hollow Au nano-balls, but not solid Au nano-particles.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the reactant object is a solid sphere
  • the obtained product is also in a form of a solid sphere
  • the reactant object is a metal plate
  • the obtained product is also a metal plate.
  • 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.
  • 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.
  • 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.
  • the thickness of the nano-plates or the nano-discs is 1-50 nm. More preferably, the thickness thereof is 1-30 nm.
  • the present invention is not particularly limited thereto.
  • 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.
  • the cross-sectional diameter thereof is 1-50 nm. More preferably, the cross-sectional diameter thereof is 1-30 nm.
  • the length of the nano-rods it can be 10-100 nm, Preferably, the length thereof is 30-100 nm.
  • the present invention is not particularly limited thereto.
  • metal foils or “metal films” means that the objects have a thickness of 0.1 ⁇ m-1000 ⁇ m, but the length, the width or the diameter thereof are not particularly limited.
  • the thickness of the metal foils or the metal films is 1 ⁇ m-500 ⁇ m.
  • the present invention is not particularly limited thereto.
  • nano-particles or “nano-spheres” means that the objects have a diameter of 1-100 nm.
  • the diameter of the nano-particles or the nano-spheres is 1-50 nm. More preferably, the diameter thereof is 1-30 nm.
  • the present invention is not particularly limited thereto.
  • the cation surfactant can be any general cation surfactant used in the art.
  • the cation surfactant is represented by the following formula (I):
  • each R 1 , R 2 , and R 3 independently is C 1-3 alkyl, R 4 is C 12-22 alkyl, and X ⁇ is a halogen ion.
  • each R 1 , R 2 , and R 3 may independently be methyl, ethyl, n-propyl, or isopropyl.
  • each R 1 , R 2 , and R 3 independently is methyl or ethyl. More preferably, all R 1 , R 2 , and R 3 are methyl or ethyl. Most preferably, all R 1 , R 2 , and R 3 are methyl.
  • R 4 can be linear or branch C 12-22 alkyl.
  • R 4 is linear C 12-22 alkyl. More preferably, R 4 is linear C 14-20 alkyl. Most preferably, R 4 is linear C 15-18 alkyl.
  • 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.
  • CTAB cetyltrimethylammonium bromide
  • 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
  • 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.
  • the purpose of replacing the first metal with the second metal can be achieved.
  • the first metal of the first metal substrate can be Ag
  • the second metal of the second metal substrate or the second metal precursor can be Au, Pd, or Pt.
  • suitable metal salts can be selected as the second metal precursor contained in the reaction solution.
  • the second metal precursor can be metal salts of Ag, Pd or Pt.
  • the second metal precursor comprises H 2 PtCl 6 , PtS 2 O 7 H 4 , HAuCl 4 , H 2 PdCl 4 , or a combination thereof, but the present invention is not limited thereto.
  • the weak reducing agent in the reaction solution is a reducing agent with reducing capacity lower than that of NaBH 4 or sodium citrate.
  • 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.
  • a specific example of the weak reducing agent is ascorbic acid (AA), i.e. vitamin C; but the present invention is not limited thereto.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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 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 ⁇ ;
  • FIGS. 10A-10B shows EDX results of metal foils according to Embodiment 5 of the present invention.
  • a colloid solution of the Ag nano-discs was diluted into a concentration of 50 ppm.
  • 600 ⁇ L of 100 mM CTAB solution, 130 ⁇ L of 100 mM AA solution and 720 ⁇ L of 5 mM HAuCl 4 solution were added therein while stirring.
  • the mixture was placed on water bath preheated at 80° C.
  • the mixture was centrifuged at 8000 rpm for 10 min, suspension was discarded and the pellet was washed and purified with saturated NaCl solution to remove AgCl precipitate. Then, the precipitate was washed for twice with de-ionized water before further characterization.
  • FIGS. 1A and 1B show the changes of the shapes and when the replacement reaction was completed.
  • TEM Transmission Electron Microscopy
  • the figures (a), (b), (c) and (d) of FIG. 1A respectively represent TEM photos of nano-discs at the reaction times of 0, 1, 8 and 16 min; and FIG. 1B shows the normalized UV-visible spectra of nano-discs obtained at the reaction times of 0, 1, 8 and 16 min.
  • FIG. 2A shows the result of the element distribution of the nano-disc determined by line-scanning before the replacement reaction was performed. After the replacement reaction was performed for 8 min, the element distributions thereof determined by line-scanning are shown in FIG. 2B . After the replacement reaction was performed for 16 min, the element distributions thereof determined by line-scanning are shown in FIG. 2C . According to the results shown in FIGS. 2A to 2C , it can be found that Ag can be completely replaced with Au as the replacement reaction times increased.
  • HR-TEM EDX High Resolution Transmission Electron Microscopy Energy-dispersive X-ray spectroscopy
  • the aforementioned results confirm that the Ag nano-discs can be completely converted into Au nano-discs in the present embodiment.
  • the obtained Au nano-discs substantially have the same shapes as the original solid shapes of reactant objects (i.e. Ag nano-discs).
  • FIGS. 3A and 3B show TEM photos of products obtained by using 0 (i.e. before the replacement reaction performed), 46, 185, 555, 720 and 741 ⁇ L of 5 mM HAuCl 4 solutions after the replacement reaction was completed; and FIG. 3B shows the normalized UV-visible spectra of products obtained by using 0 (i.e. before the replacement reaction performed), 46, 185, 555, 720 and 741 ⁇ L of 5 mM HAuCl 4 solutions after the replacement reaction was completed.
  • the optimized addition amount of 5 mM HAuCl 4 solution is 720 ⁇ L. If the addition amount thereof is less than 720 ⁇ L, the replacement reaction may not be completed. If the addition amount thereof is more than 720 ⁇ L, more HAuCl 4 may be reduced, which may cause the size of the products larger than that of the reactant objects. It should be noted that the replacement reaction is considered success in the case that the size of the products is larger than that of the reactant objects.
  • figure i shows Ag nano-decahedrons
  • figure ii shows products obtained by performing the replacement reaction for 8 min, in which partial Ag was removed to form Au/Ag hollow decahedrons
  • figure iii shows products obtained by performing the replacement reaction for 16 min, in which Ag was completely replaced with Au to form Au decahedrons.
  • figure i shows Au nanorods, in which the length and the width thereof were respectively 39 ⁇ 3 nm and 9 ⁇ 1 nm;
  • figure ii shows Au nanorods coated with Ag (Au NR@Ag), which was obtained by placing Au nanorods of figure i into silver nitrate (AgNO 3 ) solution to form Au nanorods coated with Ag shells having a thickness of 6 nm, wherein the length and the width of the Au NR@Ag were respectively 40 ⁇ 3 nm and 20 ⁇ 3 nm;
  • figure iii shows products obtained from Au NR@Ag by performing the replacement reaction for 8 min, in which partial Ag was removed to form hollow nanorods with Au/Ag alloy shells;
  • figure iv shows products by performing the replacement reaction for 16 min, wherein Ag was completely replaced with Au, the hollow structures were filled with Au to form Au nanorods, and the length and the width thereof were respectively 40 ⁇ 3 nm and 21 ⁇ 3 nm.
  • figure i shows Ag nanoprisms with a height of 68 ⁇ 4 nm
  • figure ii shows products obtained by performing the replacement reaction for 8 min, in which partial Ag was removed to form Au/Ag hollow nanoprisms
  • figure iii shows products obtained by performing the replacement reaction for 16 min, in which Ag was completely replaced with Au to form Au nanoprisms.
  • figure i shows Au nanoparticles with a size of 13 ⁇ 2 nm
  • figure ii shows Au nanoparticles coated with Ag (Au NP@Ag), which was obtained by placing Au nanoparticles of figure i into silver nitrate (AgNO 3 ) solution to form Au nanoparticles coated with Ag shells having a thickness of 6 nm
  • figure iii shows products obtained from Au NP@Ag by performing the replacement reaction for 8 min, in which partial Ag was removed to form hollow nanoparticles with Au/Ag alloy shells
  • figure iv shows products by performing the replacement reaction for 16 min, wherein Ag was completely replaced with Au, and the hollow structures were filled with Au to form Au nanoparticles. From the figures ii and iv of FIG. 4D , these results indicate that the Ag nanoparticles coated with Ag, which were served as Ag substrates, can be converted into Au nanoparticles without changing their shapes by using the method of the present invention.
  • FIGS. 5A-5C , FIGS. 6A-6C and FIG. 7 show the normalized UV-visible spectra of nanoprisms obtained at the reaction times of 0, 3 and 16 min.
  • FIGS. 5A and 6A The TEM photo and the element distribution of the nanoprisms before the replacement reaction are respectively shown in FIGS. 5A and 6A .
  • the reaction was performed for a while (3 min)
  • the TEM photo and the element distribution thereof are respectively shown in FIGS. 5B and 6B , and these results indicate that partial Ag was replaced with Pd.
  • the reaction was completed (16 min)
  • the TEM photo and the element distribution thereof are respectively shown in FIGS. 5C and 6C . According to the results shown in FIGS. 5A-5C and 6 A- 6 C, it can be found that all Ag was gradually replaced with Pd as the reaction time increased.
  • Ag foil (99.97%) having area of 4 mm 2 and thickness of 0.005 mm was used in the present embodiment.
  • the Ag foil (2 mm ⁇ 2 mm) was placed into 3.5 ml of 200 mM CTAB solution, and then 1 ml of 200 mM AA solution was added into this mixture.
  • the mixture was gently shaken using an incubator shaker in the present embodiment.
  • the present embodiment only provides a preferred manner, but the present invention is not limited thereto.
  • FIG. 8A The appearance and SEM photo (not shown in the figure) show that the Ag foil was completely converted into Au foil.
  • five different detection points on the metal foil were analyzed with HR-TEM EDX.
  • the results show that Ag elements can be detected at each detection points before the replacement reaction, as shown in FIG. 8A .
  • FIGS. 9A and 9B respectively show metal foil before and after reaction
  • FIGS. 10A and 10B respectively show EDX analysis results of metal foil before and after reaction. According to FIG. 8A to FIG. 10B , these results indicate that the Ag elements in the Ag foil can be replaced with Au elements by using the method of the present invention.

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107414069A (zh) * 2017-08-07 2017-12-01 国家纳米科学中心 银纳米圆片、其制备方法及采用其制备的金纳米环和组装体

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060235087A1 (en) * 2004-06-18 2006-10-19 Paschalis Alexandridis Preparation of metallic nanoparticles
US20080245186A1 (en) * 2005-05-13 2008-10-09 University Of Rochester Synthesis of nano-materials in ionic liquids
US20120255762A1 (en) * 2009-12-24 2012-10-11 Fujifilm Corporation Metal nanowires, method for producing same, transparent conductor and touch panel

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060235087A1 (en) * 2004-06-18 2006-10-19 Paschalis Alexandridis Preparation of metallic nanoparticles
US20080245186A1 (en) * 2005-05-13 2008-10-09 University Of Rochester Synthesis of nano-materials in ionic liquids
US20120255762A1 (en) * 2009-12-24 2012-10-11 Fujifilm Corporation Metal nanowires, method for producing same, transparent conductor and touch panel

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107414069A (zh) * 2017-08-07 2017-12-01 国家纳米科学中心 银纳米圆片、其制备方法及采用其制备的金纳米环和组装体

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