Abstract:
The present invention discloses a method for producing metal nanoparticles, in which a metallic compound is first dissolved in a solvent to obtain a metal ionic solution, then the metal ionic solution is uniformly distributed on the carrier, and finally electrons provided from an electron source are shot at the carrier for reducing the metal ions to the metal nanoparticles.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for producing nanoparticles, and particularly to a method for producing metal nanoparticles.  
         [0003]     2. Description of Related Prior Arts  
         [0004]     Recently, nanotechnology is widely developed and researched in industries and institutes to find new materials or build more efficient processes.  
         [0005]     To produce nanoparticles, some physical and chemical processes are applied, for example, redox method, photochemical method, electrochemical method, gas evaporation method and laser ablation technique. However, the currently known nanotechnologies are not good enough in many aspects such as controlling of particle size, preservation and dispersion of nanoparticles, and expensive equipment.  
         [0006]     Therefore, it&#39;s desired to provide a better process for producing metal nanoparticles to solve the above problems.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to provide a method for producing metal nanoparticles, which can be easily performed at a lower cost.  
         [0008]     A further object of the present invention is to provide a method for producing metal nanoparticles, so that the produced metal nanoparticles exhibit high dispersion, uniform particle size and can be preserved in a simple way.  
         [0009]     To achieve the above objects, the method of the present invention comprises steps of: (a) Dissolving a metallic compound in a solvent to obtain a metal ionic solution; (b) Uniformly distributing said metal ionic solution on a carrier; and (c) Shooting electrons from an electron source at said carrier for reducing said metal ions to metal nanoparticles.  
         [0010]     The metallic compound of step (a) can be a metallic salt, a metallic complex or other proper compounds, wherein the metal can be Pt, Au, Pd, Ag, Cu, Ti, Zn, Fe, Ni, Zr, Al or other proper metals. The metallic compound also can be PtCl 4 , AuCl 4 , AgNO 3 , CuSO 4  or Fe(NO 3 ) 2 .  
         [0011]     The solvent used in the present invention is not restrictedly limited and can be ultra-pure water or deionized water.  
         [0012]     Preferably, the carrier is made by a material capable of well attaching said metal ionic solution, for example, polymer, ceramic membrane, lacy carbon, non-woven fabric and carbon cloth.  
         [0013]     The metal ionic solution can be distributed on carrier by any proper method, and preferably by dipping treatment, spin coating or spray coating.  
         [0014]     In general, the above step (b) is performed at room temperature, and the carrier is further dried after distributing said metal ionic solution thereon.  
         [0015]     In the present invention, the electron source is not restrictedly limited, and can be a transmission electron microscope (TEM), a scanning electron microscope (SEM) or a DC power supply.  
         [0016]     Other features and advantages of the present invention can be understood and illustrated by the preferred embodiments accompanied with drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  shows the process for producing metal nanoparticles in accordance with the present invention;  
         [0018]      FIG. 2  is a schematic view of the dipping treatment;  
         [0019]      FIG. 3  is a schematic view of the spin coating;  
         [0020]      FIG. 4  is a schematic view of the spray coating;  
         [0021]      FIG. 5  is a BF image showing Ag nanoparticles on a polymer substrate;  
         [0022]      FIG. 6  is a SAD image showing Ag nanoparticles on a polymer substrate;  
         [0023]      FIG. 7  is a BF image showing Ag nanoparticles on lacy carbon;  
         [0024]      FIG. 8  is an appearance image of Ag nanoparticles on carbon cloth;  
         [0025]      FIG. 9  is an energy dispersive X-ray spectrum of Ag nanoparticles on carbon cloth and treated with oxidation; and  
         [0026]      FIG. 10  is a BF image showing Cu nanoparticles on a polymer substrate. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]      FIG. 1  shows the general process for producing metal nanoparticles in accordance with the present invention; which comprises the following procedures:  
         [0028]     (a) Well mixing a chemical salt in the form of powder with a proper solvent to obtain an ionic solution at a proper concentration.  
         [0029]     (b) Uniformly distributing the ionic solution on a substrate made from non-woven fabric, carbon cloth, polymer or other material capable of attaching the solution; and then drying the carrier in an oven or other suitable driers to obtain samples.  
         [0030]     (c) Positioning the samples in SEM, TEM or other suitable electron sources, and then shooting electron beam at the samples for reducing the ions to metal nanoparticles.  
         [0031]     In the above step (b), the ionic solution can be distributed by a dipping treatment, spin coating or spray coating.  FIG. 2  is a schematic view of the dipping treatment; in which a carrier  21  is dipped into an ionic solution  22 , and then picked up at a proper speed, preferably constant speed, to attach ionic solution thereon. The board arrow in  FIG. 2  indicates actions of dipping and picking up.  FIG. 3  is a schematic view of the spin coating; in which a carrier  31  is equipped and spun on a spin coating system  33  at constant velocity and an ionic solution  32  is dropped on the carrier  31 .  FIG. 4  is a schematic view of the spray coating; in which a carrier  41  is vertically located in front of a sprayer  43  at a proper distance, and a ionic solution  42  is sprayed on the carrier  41  from the sprayer  43 .  
         [0032]     To illustrate features and effects of the present invention in detailed, two Examples are exemplified as follows:  
       EXAMPLE 1  
       [0033]     The procedures are carried as follows:  
         [0034]     (a1) Well mixing AgNO 3  powders (1 g) and ultra pure water (99 ml) in a flask to prepare an Ag +  solution of 1 wt. %.  
         [0035]     (b1) Uniformly distributing the Ag +  solution on a polymeric carrier by the dipping treatment.  
         [0036]     (b2) Drying the carrier in an oven carrier and obtain a sample.  
         [0037]     (c1) Positioning the sample in the SEM and shooting electron beam on the sample for reducing the Ag +  ions to Ag metal nanoparticles. The reduction is indicated as equation (I). 
 
Ag +   +e   − →Ag  (I) 
 
         [0038]      FIG. 5  is a TEM BF image showing Ag nanoparticles reduced from an Ag +  solution of 1 wt. % on a polymer substrate, and the average particle size ranges from 38 to 41 nm.  FIG. 6  is a TEM SAD image showing Ag nanoparticles reduced from Ag +  solution of 1 wt. % on a polymer substrate, in which the Ag particles are in the form of single crystal, and grow in a prevailing direction [200].  
         [0039]     In addition to polymer, the carrier can be made from other proper material. For example,  FIG. 7  is a TEM BF image showing Ag nanoparticles reduced from an Ag +  solution on lacy carbon, which have uniform average particle size about 4˜6 nm and exhibits good dispersion.  FIG. 8  shows the exterior of Ag nanoparticles reduced from an Ag +  solution of 1 wt. % on carbon cloth, which is taken with FESEM (field emission scanning electron microscope). The Ag nanoparticles have uniform average particle size about 7˜8 nm and exhibit good dispersion.  
         [0040]      FIG. 9  is an energy dispersive X-ray spectrum of Ag nanoparticles reduced from an Ag +  solution of 1 wt. % on carbon cloth and further treated with oxidation. As shown in the spectrum, Ag nanoparticles are oxidized to Ag 2 O, and signals of Cu and C are generated by the sample support and carbon cloth.  
       EXAMPLE 2  
       [0041]     Repeat the procedures of Example 1, but replace AgNO 3  with CuSO 4  to prepare a cupric solution of 1 wt. % which is then distributed on a polymer membrane by spin coating. Cu nanoparticles are eventually obtained by shooting electron beam to the sample from an e-gun of TEM.  
         [0042]      FIG. 10  is a TEM BF image showing Cu nanoparticles with uniform particle size about 6˜7 nm and good dispersion.  
         [0043]     According to the above embodiments, it&#39;s obvious that properties such as dispersion and particle size, can be varied by controlling concentration of the ionic solution. That is, the present invention provides a practical and simple process for producing nanoparticles.  
         [0044]     In the present invention, the carrier is preferably made from a material easily attached with the ionic solution. As for other material, physical or chemical treatments may be used to promote attachment therebetween. The physical treatments include ion bombardment, plasma modification and thermal process; and the chemical treatments include coating with organic or inorganic solution, implanting ionphilic bond and chemical corrosion. For example, an ionic solution dropped on an uneasily-attached polymer substrate typically presents half-spherical shape under a contact angle system. However, much larger contact areas between the solution and the substrate bombarded with Ar ions will be observed, which indicates attachment therebetween is promoted.  
         [0045]     According to the method of the present invention, metal ions can be easily reduced to metal nanoparticlas by shooting electron beam from a proper electron source, which costs lower than traditional technologies. Moreover, the metal nanoparticles produced exhibit advantages of good dispersion and uniform particle size and can be easily preserved.  
         [0046]     The metal nanoparticles can be further oxidized, and thus oxide particles, for example, TiO 2 , ZnO, Ag 2 O, CuO, ZrO 2 , NiO and Al 2 O 3  can be produced for suitable applications. In addition to traditional industries, for example, catalyst manufacturing, textile industry, metal or non-metal industry, the present invention is suitable for applying to nanotech industries, for example, bio-chip, membrane and electrode assembly (MEA), cosmetics, bio-medical materials.  
         [0047]     While the present invention has been illustrated by the preferred embodiments aforementioned, scope of the invention should not be limited therewithin but refer to the appended claims.