TW201330955A - Manufacturing method of precious metal nanoparticles - Google Patents

Abstract

This invention provides a one pot method, which is relatively more eco-friendly and facile than other kinds of wet chemical methods, to synthesize gold and silver nanoparticles. The seeds, synthesized by other chemical reactions prior to the photochemical reaction, were not needed in this method. Gold nanoparticles and silver nanoparticles can citrate and the mixtures of AgNO3 and sodium citrate, respectively, with the sodium lamp or LEDs. The silver ions and AuCl4- ions were reduced by the citrate ions to form silver and gold seeds, respectively, in the initial stage via a photo-assisted reduction process under the light irradiation. By continuously irradiating the seed colloids, the seeds can grow gradually, via the plasmon-mediated reduction process, into the larger nanoparticles with highly crystalline structures. Not only the sizes of the nanoparticles prepared by the methods of this invention were mono-dispersed, but also the shapes can be adjusted by varying the bathed temperatures and exciting wavelengths.

Description

Method for producing noble metal nanoparticles

The present invention provides a method for producing noble metal nanoparticles, which uses a photochemical synthesis method to synthesize gold or silver nanoparticles using a one-pot reaction solution without additional seeding.

Gold and silver nanoparticles have been widely used in antibacterial, chemical or biological sensing, cell or tissue imaging, photoelectric elements, catalytic reactions, and surface enhanced Raman spectroscopy because of their unique physicochemical properties. on.

A variety of methods for synthesizing gold and silver nanoparticles have been developed, among which the wet chemical method has a large number of properties for preparing highly homogeneous gold and silver nanoparticles. The wet chemical method can be divided into electrochemical method, chemical reduction method, sonophoresis method and photochemical method according to the principle of synthesis. Among them, photochemical method can theoretically achieve the purpose of reaction by irradiating sunlight, and is considered to have an environment. Friendly advantage. Therefore, the development of photochemical synthesis methods of nano gold or nano silver can meet the current spirit of green chemistry and environmental sustainability.

In the past, in the technique of synthesizing gold and silver nanoparticles by photochemical method, since surface plasmons acting on light are required, it is necessary to first use chemical synthesis to produce metal nanoparticles of appropriate size as seed crystals. This chemical method often requires the use of a strong reductant, such as sodium borohydride (NaBH ₄ ), to reduce the metal ions to obtain seed crystals, but such seed crystal production methods will encounter some problems: (1) strong reduction Improper use of the agent may cause operator or ecological hazard; (2) Strong reducing agent needs to be added at an appropriate rate to produce an appropriate size seed crystal. This operation requires resistance and technology, resulting in each batch of nano particles. The quality (type and size distribution) is unstable; (3) due to the need to add a reducing agent to produce seed crystals, which is a time-consuming and labor-intensive procedure, this method suffers from problems that cannot be generated in large quantities.

In order to overcome the shortcomings of the above three photochemical synthesis methods, the inventors succeeded in developing a photochemical synthesis method that does not require a seed crystal, and the synthesis method has the characteristics of environmental protection, mass production, simple operation, and high repeatability.

The main object of the present invention is to provide a method for producing noble metal nanoparticles, which can improve the synthesis steps of photochemical methods, and overcome the different quality of precious metal nanoparticles in each reaction and the manufacturing process due to the process of seed crystal synthesis. The chemical reduction method is complicated and the like, and the invention eliminates the step of synthesizing the seed crystal by the strong reducing agent, and is more convenient for industrial mass production because of simplifying the process thereof, and the present invention does not need to add a strong reducing agent which is harmful to the environment. The method provided by the invention is more environmentally friendly.

A secondary object of the present invention is to propose a photochemical synthesis method of noble metal nanoparticles, wherein the synthesized nanoparticles have high uniformity of size and can maintain their morphology for several months.

In order to achieve the above-mentioned various objects, the present invention provides a method for producing noble metal nanoparticles, which comprises the following steps:

(a) preparing a noble metal ion solution;

(b) preparing a photoreducing agent;

(c) mixing a precious metal ion solution with a photoreducing agent to form a mixed solution;

(d) controlling the solution at a specific reaction temperature;

(e). Providing a light source to reduce the noble metal clusters in the mixed solution to the noble metal nanoparticles by sodium citrate.

The metal of the metal ion solution contemplated above may be, but not limited to, gold (Au) or silver (Ag). The ion source is, for example, tetrachloroauric acid (HAuCl ₄ ), silver nitrate (AgNO ₃ ) or the like. The solution can be ultrapure water or deionized water. The photoreducing agent can be, but not limited to, sodium citrate.

The above reaction temperature is controlled between 0 and 100 degrees Celsius, and the wavelength of the light source is between 200 and 800 nm. Under the illumination of a suitable light source, the metal ions can be reduced by sodium citrate. This process is called "light-assisted lemon". Acid reduction process, this process can occur without metal nanocrystals. Continuous illumination will cause the seed crystal to gradually grow and further form crystal nanoparticles with good crystal shape. When the wavelength of the light source provided is in the range of 400 to 500 nm, the reaction speed is better, and the shape of the product may be changed according to the regulation of the concentration of silver or gold ions. When the wavelength of the light source is at 450 nm and the concentration is 10 ^-4 , the silver nanoparticles are mainly decahedron, and the gold nanoparticles are spherical. At a concentration of 10 ^-3 , silver nanoparticles or gold nanoparticles are Focus on the sphere.

The noble metal nanoparticles obtained according to the present invention can have excellent particle size uniformity according to different manufacturing conditions, and the particle size can be stably maintained for more than one year. In addition, the invention has the advantages of simple manufacturing process, uniform quality of different reaction batches and conforming to the concept of environmental protection, and overcomes three shortcomings in the synthesis of general photochemical methods, so that the photochemical method is more industrially manufactured for noble metal nanoparticles. As possible.

1 is a flow chart of a method for manufacturing precious metal nanoparticles of the present invention, which mainly comprises the following steps:

(a). Preparing a precious metal ion solution,

(b). preparing a photoreducing agent,

(c) mixing a precious metal ion solution with a photoreducing agent to form a mixed solution,

(d). Control the mixed solution at a specific reaction temperature,

(e). Providing a light source to reduce the noble metal clusters in the mixed solution to the noble metal nanoparticles by sodium citrate.

The precious metal ion solution of the above step (a) includes, but is not limited to, gold ions or silver ions, and the ion source includes tetrachloroauric acid (HAuCl ₄ ), silver nitrate (AgNO ₃ ), and the like. The solvent can be ultrapure water or deionized water. The ion source can be dissolved in the solvent during preparation.

The photoreducing agent of the above step (b) is sodium citrate. In the method of the present invention, sodium citrate can be used as a stabilizer for the reaction, in addition to being a photoreducing agent.

In the case of a photoreducing agent, when there is no citrate present, the illumination does not reduce the silver ion or the tetrachloroauric acid ion to form a nanoparticle, in the case where only citrate and silver ion or tetrachloroauric acid ion are mixed. Under the condition that the solution of the metal nanoparticles can not be observed for a while at room temperature, when the light and the citrate are simultaneously present, the synergistic effect is to reduce the silver ions or the tetrachloroauric acid ions into silver nanoparticles or gold. Nano seed crystals. We call this synergistic effect "photo-assisted citrate reduction process", in which a metal ion cluster or a complex formed by citrate and metal ions can be combined with visible light. The effect, although the coefficient of action is so small that there is no way to exhibit an observable absorption value in the ultraviolet visible spectrum, however, only a small fraction of the energy of the photon captured by the cluster or complex promotes citrate. The reduction occurs, so that the citrate reduces the metal ions to nanocrystals with the aid of light.

The seed crystal produced by the above method has better crystallinity than the seed crystal produced by the general chemical reduction method, and further crystallizing, the crystal crystal having better crystallinity can be gradually grown by the photochemical reaction of the plasmonic medium. Since the surface plasmons react with the incident light to generate a spatially anisotropic local electric field, which promotes uneven distribution of ions in the surrounding liquid, the crystal grows into a non-spherical nanostructure. The shape and size of these nanostructures can be controlled by controlling temperature and wavelength of illumination.

On the other hand, the citrate ion and other charged products provided by sodium citrate will adsorb on the surface of the metal nanoparticles to make it negatively charged, thus making the nanoparticles repel each other due to the same charge, so that the metal nanoparticle can be stabilized. The particles are suspended in the solution to avoid aggregation and precipitation.

The reaction temperature of the above step (d) is controlled between 0 and 100 degrees, and can be adjusted according to different embodiments.

The light source of the above step (e) may be provided by an LED, a halogen lamp, a sodium lamp or a UV lamp. The wavelength of the light source used in the present invention is between 200 and 800 nm, since the LED is a single wavelength light source provider which is inexpensive and superior in performance. Therefore, the preferred embodiment cited is a light source used for the reaction of the LDE lamp source. Since the electric field formed by the surface plasmon has directionality, the growth of the metal nanoparticle will exhibit spatial non-uniform growth, which is provided at this time. The source wavelength further controls the size and shape of the synthetic metal nanoparticles, and thus different wavelengths can be reacted in accordance with various embodiments. The method for producing the noble metal nanoparticles of the present invention can be fully understood from the following description of the preferred embodiments, and can be accomplished by those of ordinary skill in the art. However, the embodiments of the present invention are not limited to the following embodiments.

Embodiment 1

(a1) 17 mg of silver nitrate (AgNO ₃ ) powder was weighed by an electronic balance and uniformly mixed in 10 ml of deionized water (H ₂ O) to form a silver nitrate solution having a concentration of 10 ^-2 M.

(b1) 1.32 g of sodium citrate was weighed by an electronic balance, and uniformly dissolved in 990 ml of deionized water (H ₂ O) to prepare an aqueous solution of 4.53 x 10 ^-3 M sodium citrate.

(c1) A silver nitrate solution and an aqueous sodium citrate solution were mixed and stirred with a magnetic stirrer for 5 minutes to sufficiently mix sodium citrate with silver nitrate.

(d1) The reaction temperature was controlled at room temperature.

(e1) The mixed solution was placed under an LED light source having a wavelength of 450 nm, and the reaction became pink after the illumination was continued for about 1.5 hours to complete the reaction.

The transmission electron microscope image obtained in this embodiment is shown in FIG. 2, which is a magnified photograph of the silver nanoparticle particles seen at a magnification of 12000 times. As is apparent from FIG. 2, the method of the present invention is on this embodiment. A large number of silver decahedral nanoparticles are obtained with high particle shape specificity and particle size uniformity.

Refer to Figure 3 for the color change process of the solution in this example. It is a UV-visible absorption spectrum sample taken over time. It can be observed that the solution will have the highest absorption peak of 500 nm at 1.5 hours of illumination time. This absorption peak is a silver decahedron. The long axis signal provided by the nanoparticle.

The stability of the silver nanoparticle synthesized in this embodiment can be shown in FIG. 4, and FIG. 4(A) is a transmission electron microscope image of the decahedral silver nanoparticle synthesized in this embodiment for 2 months, FIG. 4 ( B) The decahedral silver nanoparticle synthesized in this embodiment is placed in a transmission electron microscope image for one year, and it can be seen that it still has a certain ten-faced in vitro type and particle size, indicating that the method is synthesized by the silver mine. Rice particles have good stability.

Embodiment 2

(a2) 394 mg of tetrachloroauric acid (HAuCl ₄ ‧3H ₂ O) powder was weighed by electronic balance and uniformly mixed in 100 ml of deionized water (H ₂ O) to form tetrachlorogold at a concentration of 10 ^-2 M. Acid solution.

(b2) 1.32 g of sodium citrate was weighed by an electronic balance, and uniformly dissolved in 900 ml of deionized water (H ₂ O) to prepare an aqueous solution of 4.99 x 10 ^-3 M sodium citrate.

(c2) A tetrachloroauric acid solution and an aqueous solution of sodium citrate were mixed and stirred with a magnetic stirrer for 5 minutes to sufficiently mix tetrachloroauric acid with silver nitrate.

(d2) The reaction temperature was controlled at room temperature.

(e2) The mixed solution was placed under an LED light source having a wavelength of 450 nm, and the reaction was turned into pink after the illumination was continued for about 1.5 hours to complete the reaction.

The transmission electron microscope image obtained in this embodiment is shown in FIG. 5, which is an enlarged photograph of the gold nanoparticle particles seen at a magnification of 20,000 times. As apparent from FIG. 5, the method of the present invention is on this embodiment. A large number of gold nanospheres are available, and the particle size is about 10 nm on average.

In combination with the above two preferred embodiments, the method of the present invention can provide metal nanoparticles having high shape specificity and uniformity of particle size, and has good stability. Compared with the prior photochemical synthesis technology, the method of the present invention has The following advantages:

(1) It is not necessary to synthesize seed crystals in advance, so that the more complicated seed crystal synthesis steps in the photochemical synthesis technology are omitted, and the slight differences caused by the seed crystal synthesis process are removed, resulting in the quality of each batch of metal nanoparticles ( Type and size distribution) are unstable.

(2) The synthesis step and the apparatus and the medicament used in the method of the invention are relatively simple, no additional protective agent and reducing agent are added, and the environmental impact is alleviated, so that the synthesis process is more environmentally friendly.

The above-mentioned methods are only the preferred embodiments of the present invention, and are not intended to limit the present invention; all other equivalent modifications or substitutions that are not departing from the spirit of the present invention should be included in the scope of the following claims. .

Figure 1 is a flow chart showing a method for producing noble metal nanoparticles of the present invention.

Figure 2: Transmissive electron microscope image of Example 1.

Figure 3: UV-visible absorption spectrum of the sample taken over time in Example 1.

Figure 4 (A): A transmission electron microscope image (I) of the silver nanoparticle of Example 1 after being left for a period of time.

Figure 4 (B): Transmissive electron microscope image of the silver nanoparticle of Example 1 after being placed for a period of time (2).

Figure 5: Transmissive electron microscope image of Example 2.

Claims (11)

A method for producing a noble metal nanoparticle, comprising: (a) preparing a noble metal ion solution; (b) preparing a photoreducing agent; (c) mixing a noble metal ion solution with a photoreducing agent to form a mixed solution; Controlling the mixed solution at a specific reaction temperature; (e). Providing a light source to reduce the precious metal clusters in the mixed solution to the noble metal nanoparticles by sodium citrate. The method for producing a noble metal nanoparticle according to the first aspect of the invention, wherein the photoreducing agent is sodium citrate. According to the method for producing a noble metal nanoparticle according to the first aspect of the patent application, the particle size of the noble metal nanoparticles synthesized is 10 to 200 nm. According to the method for producing a noble metal nanoparticle according to the first aspect of the patent application, the reaction temperature is from 0 to 100 degrees. The method for producing a noble metal nanoparticle according to any one of claims 1 to 4, wherein the noble metal ion contains gold ions and silver ions. According to the method for producing a noble metal nanoparticle according to the fifth aspect of the patent application, the noble metal ion concentration is from 10 to 5000 μM. A method for producing a noble metal nanoparticle according to claim 5, wherein the silver ion is derived from silver nitrate. A method for producing a noble metal nanoparticle according to claim 5, wherein the gold ion is derived from tetrachloro acid. According to the method for producing a noble metal nanoparticle according to the fifth aspect of the patent application, the light source has a wavelength in the range of 200 to 800 nm. According to the method for producing a noble metal nanoparticle according to claim 9 of the patent application, the wavelength of the light source is preferably 400 to 500 nm. According to the method for producing a noble metal nanoparticle according to claim 10, the wavelength of the light source is preferably 450 nm.