Preparation method of anisotropic gold nanoparticles

Abstract

The invention belongs to the field of materials, and discloses a preparation method of anisotropic gold nanoparticles, which comprises the step of performing plasma radiation on a mixed solution of acid or salt containing gold element, a surfactant and ethanol to obtain the anisotropic gold nanoparticles. The anisotropic gold nanoparticles can be rapidly synthesized in one step through plasma radiation of a mixed solution of gold-containing acid or salt, a surfactant and ethanol, and the obtained gold nanoparticles can stably exist in the solution in a colloidal form; the preparation is carried out through interaction between plasma and a mixed solution, the overall energy consumption is low, and environmental friendliness is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of materials and relates to a method for preparing anisotropic gold nanoparticles, in particular to a method for preparing anisotropic gold nanoparticles by adopting a plasma electrochemical method. Background Art

[0002] Plasma is the fourth state of matter besides solid, liquid and gas. It contains roughly equal numbers of positive and negative charges and is electrically neutral to the outside. In addition to positive and negative charges, there are a large number of excited substances in plasma, which have strong reactivity and are widely used in the semiconductor industry, material synthesis and material surface modification.

[0003] Metal nanomaterials are aggregates of metal atoms with a size of 1-100 nanometers, which is smaller than the wavelength of light. Due to their small size, quantum confinement effects occur, and increasing or decreasing the number of metal atoms will cause significant changes in their structure, electronic and optical properties. Unlike macroscopic metal materials, the size, morphology and element distribution of metal nanoparticles determine their mechanical behavior, surface adsorption, transport, catalytic activity and photoelectric properties. The shape of metal nanoparticles can be used to regulate the absorption wavelength of their localized surface plasmon resonance (LSPR), thereby promoting the application of metal nanoparticles. Anisotropic gold nanoparticles have excellent optical properties and have therefore received widespread attention.

[0004] The wet anisotropic growth of metal nanoparticles is generally a two-step synthesis method: first, gold nanocrystals are formed in the solution through rapid reduction, then certain crystal faces of these crystals are covered with a specific surfactant, and then the gold element in the solution is slowly reduced to finally obtain anisotropic gold nanoparticles. However, this preparation method is relatively complicated and has a low synthesis efficiency.

[0005] Plasma electrochemistry can also be used to synthesize gold nanoparticles, but the gold nanoparticles synthesized are generally spherical. So far, there has been no report on the controllable anisotropic growth of gold nanomaterials based on plasma electrochemistry.

[0006] Therefore, it is very necessary to develop a new method for preparing anisotropic gold nanoparticles. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing anisotropic gold nanoparticles. By plasma irradiating a mixed solution of an acid or salt containing gold elements, a surfactant and ethanol, the anisotropic gold nanoparticles can be quickly synthesized in one step, and the obtained gold nanoparticles can stably exist in the solution in a colloidal form; the preparation is carried out by using the interaction between plasma and the mixed solution, the overall energy consumption is low, and it is environmentally friendly.

[0008] One of the purposes of the present invention is to provide a method for preparing anisotropic gold nanoparticles, the preparation method comprising:

[0009] A mixed solution of an acid or salt containing gold element, a surfactant and ethanol is subjected to plasma irradiation to obtain anisotropic gold nanoparticles.

[0010] In the present invention, the plasma radiation method is adopted to prepare gold nanoparticles. The prepared gold nanoparticles not only have high purity and anisotropy, but also can stably exist in the solution in the form of colloid for a long time.

[0011] In the present invention, the plasma radiation method is adopted for preparation, which not only has a simple synthesis device, but also has a simple synthesis method, high synthesis efficiency, and can be synthesized in one step.

[0012] In the present invention, when the acid or salt containing the gold element in the mixed solution is subjected to plasma radiation, the positive-valent gold element can be reduced to form zero-valent gold particles.

[0013] In the present invention, the surfactant plays two roles in the process of preparing anisotropic gold nanoparticles: one is to regulate the anisotropic growth of the nanoparticles, and the other is to act as a stabilizer to enable the synthesized nanoparticles to be stable in the solution in a colloidal form.

[0014] In the present invention, the surfactant and ethanol act together to enable the gold nanoparticles to achieve anisotropic growth during the synthesis process, thereby greatly expanding the scope of application and application prospects of the gold particles. During the growth process of the gold nanoparticles, the surfactant of a specific type can be adsorbed on a specific crystal face to prevent the growth of the crystal face, thereby achieving anisotropic growth, and the ethanol decomposes under the action of plasma to obtain some free radicals with high reduction activity, such as hydrogen atoms, hydrogen peroxide, etc., which can accelerate the reduction of the gold element. The combination of ethanol and the surfactant can achieve rapid anisotropic synthesis of gold nanoparticles.

[0015] In the present invention, the preparation method of the mixed solution comprises: placing an acid or salt containing gold element, a surfactant and ethanol in water to obtain a mixed solution.

[0016] In the present invention, in the mixed solution, the molar ratio of gold element to surfactant is 1:(0.5-2.5), for example, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, etc.

[0017] In the present invention, in the mixed solution, the volume fraction of ethanol is 0-4% (eg 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 3.9%, etc.), but does not include 0% and 4%.

[0018] In the present invention, the surfactant and ethanol work together to enhance the anisotropic growth of gold nanoparticles. When the surfactant and ethanol are added within a specific ratio range, the two have a better synergistic effect.

[0019] In the present invention, the surfactant includes cetyltrimethylammonium bromide.

[0020] In the present invention, the acid containing gold element is chloroauric acid.

[0021] In the present invention, the salt containing gold element is chloroaurate.

[0022] In the present invention, the plasma radiation is achieved by a plasma electrochemical circulation device;

[0023] Wherein, the plasma electrochemical cycle device comprises:

[0024] A container for holding a mixed solution;

[0025] Plasma electrochemical device for the synthesis of anisotropic gold nanoparticles;

[0026] A monitoring device for monitoring the synthesis of anisotropic gold nanoparticles;

[0027] The container, the plasma electrochemical device and the monitoring device are connected in series via a pipeline;

[0028] The mixed solution flows under the driving of the driving device.

[0029] In the present invention, the mixed solution in the container is transported to the plasma electrochemical device through a pipeline under the action of a driving device, and is irradiated by plasma when overflowing the surface of the plasma electrochemical device, so that the gold element in the mixed solution is reduced and anisotropic gold nanoparticles are formed under the action of a surfactant and ethanol; under the action of the driving device, the mixed solution is transported to a monitoring device for real-time detection.

[0030] In the present invention, the temperature of the mixed solution in the container is 20-30°C, for example, 20°C, 22°C, 25°C, 28°C, 30°C, etc., preferably 25°C. The present invention does not specifically limit the specific structure or composition of the container, and those skilled in the art can adjust it according to actual needs, as long as it meets the functions of holding liquid and controlling temperature; the present application is used to control the temperature of the mixed solution by placing the container in a constant temperature water bath.

[0031] In the present invention, the plasma electrochemical device includes a first electrode and a second electrode; when the plasma electrochemical device is working, the first electrode is located in the mixed solution, and the second electrode is located 2-5 mm (for example, 2 mm, 3 mm, 4 mm, 5 mm, etc.) above the upper surface of the mixed solution; voltage is applied to the first electrode and the second electrode, and the gas between the surface of the mixed solution and the second electrode is broken down to generate a discharge plasma, and the mixed solution overflowing the surface of the plasma electrochemical device is radiated.

[0032] In the present invention, the materials of the first electrode and the second electrode are independently any one of semiconductor materials, metal materials or carbon materials;

[0033] The second electrode is a tubular electrode or a solid electrode;

[0034] When the second electrode is a tubular electrode, gas is introduced into the pipe, and after voltage is applied, the gas generates discharge plasma.

[0035] In the present invention, the first electrode acts as an inert electrode, and the second electrode acts as a plasma discharge electrode. As a preferred embodiment of the present invention, the first electrode is a graphite electrode, the second electrode is a tubular tungsten steel electrode, and argon gas is introduced into the pipe of the second electrode; after applying a voltage exceeding the breakdown voltage of argon gas, a large amount of atmospheric pressure argon plasma can be generated above the overflowed mixed solution, thereby reacting with the gold element to produce gold nanoparticles.

[0036] In the present invention, the voltage applied between the first electrode and the second electrode is higher than the breakdown voltage of the gas, so that the gas can generate a discharge plasma after breakdown; the reaction time is 20-40 minutes (for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, etc.); wherein, the power source used for the applied voltage may be direct current, alternating current or pulsed power, and this application does not limit the power source, and those skilled in the art may adjust it according to actual needs.

[0037] In the present invention, the monitoring device comprises a cuvette, a light source and an absorption spectrometer, the cuvette is used to collect mixed solution samples, and the absorption spectrometer is used to detect the absorption spectrum.

[0038] The second object of the present invention is to prepare anisotropic gold nanoparticles through the preparation method of the first object.

[0039] In the present invention, the prepared anisotropic gold nanoparticles have absorption peaks at 530-560nm and 740-820nm in the absorption spectrum.

[0040] In the present invention, the anisotropic gold nanoparticles can regulate the wavelength of plasma resonance absorption on the local surface and have good optical properties, and therefore have good application prospects in the field of optics.

[0041] Technical features and beneficial effects of the present invention:

[0042] In the present invention, anisotropic gold nanoparticles can be quickly synthesized in one step by irradiating a mixed solution containing chloroauric acid, a surfactant and ethanol with plasma, and the obtained gold nanoparticles can stably exist in the solution in a colloidal form; the preparation is carried out by using the interaction between plasma and the mixed solution, the overall energy consumption is low, and the environment is friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the structure of a plasma electrochemical cycle device;

[0044] Among them, 1 is a container, 2 is a plasma electrochemical device, 3 is a monitoring device, 4 is a mixed solution, 5 is a pipeline, and 6 is a driving device;

[0045] Figure 2 For comparison in Experiment 1, the absorption spectra of chloroauric acid solution treated with plasma containing mixed solutions of ethanol with different concentrations and without surfactant;

[0046] Figure 3 For comparison in Experiment 2, the absorption spectra of the mixed solution with ethanol added and without ethanol added in plasma-treated chloroauric acid solution;

[0047] Figure 4 The absorption spectra of mixed solutions of surfactants with different concentrations in plasma-treated chloroauric acid solutions in Examples 1-6 and Comparative Experiment 1 are shown. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0049] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific examples. If the specific experimental conditions are not specified in the examples, they are usually in accordance with conventional conditions or the conditions recommended by the reagent company; the raw materials, reagents, consumables, etc. used in the following examples, unless otherwise specified, can be obtained through commercial channels.

[0050] Equipment Examples

[0051] The present application provides a plasma electrochemical cycle device, such as Figure 1As shown, it includes: a container 1, a plasma electrochemical device 2 and a monitoring device 3;

[0052] The container 1 is used to hold the mixed solution 4, and the container 1 is placed in a constant temperature water bath at 20-30°C (taking 25°C as an example) to ensure the temperature of the mixed solution;

[0053] The plasma electrochemical device 2 has a graphite rod with a diameter of 5 mm placed at the bottom of the solution as an inert electrode (i.e., the first electrode), a hollow tungsten steel electrode with a slightly conical nozzle, an inner diameter of 1.02 mm, and an outer diameter of 6.35 mm as the second electrode, and argon gas with a flow rate of 50 sccm is introduced into the cavity of the second electrode; the first electrode is located in the mixed solution, and the distance between the second electrode and the liquid surface of the mixed solution is 3 mm.

[0054] A positive DC voltage is applied to the first electrode and the second electrode, and the mixed solution is used as a discharge cathode. When the applied voltage exceeds the breakdown voltage of argon gas, an atmospheric pressure argon plasma can be generated above the flowing mixed solution.

[0055] The monitoring device 3 includes a cuvette, a deuterium halogen lamp and a spectrometer. The spectrometer performs real-time absorption spectrum detection on the synthesized nano-gold solution contained in the flow path.

[0056] The container 1, the plasma electrochemical device 2 and the monitoring device 3 are connected by a pipeline 5, and the mixed solution 4 is transported under the drive of a driving device 6 (taking a peristaltic pump as an example, the inner diameter is 3mm, the outer diameter is 5mm, and the flow rate of the driving mixed solution is 100mL / min).

[0057] Example 1

[0058] This embodiment provides a method for preparing gold nanoparticles, comprising:

[0059] (1) adding chloroauric acid, surfactant hexadecyltrimethylammonium bromide and ethanol into water to form a mixed solution, wherein the concentration of chloroauric acid is 0.4 mM, the concentration of the surfactant is 0.5 mM, and the volume fraction of ethanol is 0.5%;

[0060] (2) placing the mixed solution in a container of the plasma electrochemical circulation device in the structural example, maintaining the temperature at 25° C. with a water bath, transporting the mixed solution to the plasma electrochemical device under the action of a peristaltic pump, applying a voltage to the first electrode and the second electrode, wherein the applied voltage exceeds the breakdown voltage of argon gas, thereby generating a large amount of atmospheric pressure argon plasma above the flowing mixed solution;

[0061] (3) Atmospheric pressure argon plasma reacts with the gold element in the mixed solution to prepare anisotropic gold nanoparticles.

[0062] Embodiment 2-6

[0063] The difference from Example 1 is that the concentrations of cetyltrimethylammonium bromide are 0.2 mM, 0.4 mM, 0.6 mM, 0.8 mM and 1 mM respectively, and the other concentrations and preparation methods are the same as those in Example 1.

[0064] Example 7

[0065] This embodiment provides a method for preparing gold nanoparticles, comprising:

[0066] (1) adding sodium chloroaurate, surfactant hexadecyltrimethylammonium bromide and ethanol into water to form a mixed solution, wherein the concentration of sodium chloroaurate is 0.4 mM, the concentration of the surfactant is 0.2 mM, and the volume fraction of ethanol is 0.5%;

[0067] (2) placing the mixed solution in a container of the plasma electrochemical circulation device in the structural example, maintaining the temperature at 25° C. with a water bath, transporting the mixed solution to the plasma electrochemical device under the action of a peristaltic pump, applying a voltage to the first electrode and the second electrode, wherein the applied voltage exceeds the breakdown voltage of argon gas, thereby generating a large amount of atmospheric pressure argon plasma above the flowing mixed solution;

[0068] (3) Atmospheric pressure argon plasma reacts with the gold element in the mixed solution to prepare anisotropic gold nanoparticles.

[0069] Example 8

[0070] This embodiment provides a method for preparing gold nanoparticles, comprising:

[0071] (1) adding potassium chloroaurate, surfactant hexadecyltrimethylammonium bromide and ethanol into water to form a mixed solution, wherein the concentration of potassium chloroaurate is 0.4 mM, the concentration of the surfactant is 1 mM, and the volume fraction of ethanol is 3.9%;

[0072] (2) placing the mixed solution in a container of the plasma electrochemical circulation device in the structural example, maintaining the temperature at 25° C. with a water bath, transporting the mixed solution to the plasma electrochemical device under the action of a peristaltic pump, applying a voltage to the first electrode and the second electrode, wherein the applied voltage exceeds the breakdown voltage of argon gas, thereby generating a large amount of atmospheric pressure argon plasma above the flowing mixed solution;

[0073] (3) Atmospheric pressure argon plasma reacts with the gold element in the mixed solution to prepare anisotropic gold nanoparticles.

[0074] In order to further explore the effects of surfactant and ethanol concentration on the anisotropic growth of gold nanoparticles, the following comparative experiments were conducted:

[0075] Comparative experiment 1:

[0076] The mixed solution does not contain the surfactant hexadecyltrimethylammonium bromide. When the concentration of chloroauric acid added to water is 0.4mM and the concentration of ethanol is 0-4%, the plasma irradiation is carried out for 30 minutes and the real-time measurement is carried out by the monitoring device. The results are shown in Figure 2 In (a)-(e), at different ethanol concentrations (0%, 0.5%, 1%, 2%, 4%), the absorption spectrum of the plasma-treated solution changes with the treatment time. It can be clearly seen that there is an absorption peak around 530-560nm, which is the localized plasma resonance absorption peak unique to gold nanoparticles, indicating that the plasma does reduce the gold element in chloroauric acid and synthesizes gold nanoparticles in the solution. The characteristic absorption peak intensity of the gold nanoparticles is positively correlated with the concentration of gold nanoparticles in the solution. Figure 2 (f) shows the change of the characteristic absorption peak intensity of gold over time under different ethanol concentrations. It can be seen that alcohol with a volume fraction of 0.5% accelerates the synthesis of gold nanoparticles, but excessive ethanol will also inhibit the synthesis of gold nanoparticles in the solution.

[0077] Comparative experiment 2:

[0078] A comparative experiment was set up to compare the auxiliary effect of ethanol. Specifically, two experiments were included. The first experiment included: adding surfactant hexadecyltrimethylammonium bromide to the aqueous solution of chloroauric acid to obtain a mixed solution: the concentration of chloroauric acid was 0.4mM, and the concentration of surfactant hexadecyltrimethylammonium bromide was 0.5mM. The plasma was irradiated for 30 minutes, and real-time measurements were performed through a monitoring device. The results are shown in Figure 3 , the plasma-treated solution obtained two absorption peaks, one near 530nm and the other near 740nm, indicating that anisotropically grown gold nanoparticles were formed in the solution. The second experiment was to add an additional 0.5% volume fraction of ethanol to the above mixed solution. After plasma treatment, not only did the absorption peak position at the long wavelength change from 740nm to 815nm, but the ratio of long-wave to short-wave peak intensities was also enhanced. The enhanced ratio of long-wave to short-wave peak intensities indicates that the proportion of anisotropic nanoparticles in the solution has increased, which means that ethanol increases the growth rate of anisotropic gold nanoparticles.

[0079] Figure 4 The results are a comparison of multiple groups of experiments in Examples 1-6 and Comparative Example 1, that is, the absorption spectrum test results of reaction solutions of cetyltrimethylammonium bromide with different concentrations after plasma treatment; Figure 4It can be seen that for the chloroauric acid solution containing 0.5% volume ethanol, when the concentration of cetyltrimethylammonium bromide is in the range of 0.2-1.0 mM, the solution after plasma treatment has two absorption peaks, which indicates that anisotropically grown gold nanoparticles are obtained in the solution.

[0080] Comparative Experiment 3-4

[0081] The surfactant cetyltrimethylammonium bromide in Example 1 was replaced by polyvinyl pyrrolidone and sodium dodecyl sulfate, respectively, and the rest of the preparation method was the same as that in Example 1.

[0082] By comparing Example 1 with Comparative Examples 3-4, it can be found that only by using the specific surfactant cetyltrimethylammonium bromide of the present application can anisotropic gold nanoparticles be obtained, which cannot be achieved by using other surfactants.

[0083] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing anisotropic gold nanoparticles, characterized in that: The preparation method comprises: A mixed solution of an acid or salt containing gold element, a surfactant and ethanol is subjected to plasma irradiation to obtain anisotropic gold nanoparticles.

2. The preparation method according to claim 1, characterized in that: The preparation method of the mixed solution comprises: placing an acid or salt containing gold element, a surfactant and ethanol in water to obtain a mixed solution; In the mixed solution, the molar ratio of gold element to surfactant is 1:(0.5-2.5); In the mixed solution, the volume fraction of ethanol is greater than 0% and less than 4%.

3. The preparation method according to claim 2, characterized in that: The surfactant is cetyltrimethylammonium bromide; The acid containing the gold element is chloroauric acid; and the salt containing the gold element is chloroaurate.

4. The preparation method according to claim 1, characterized in that: The plasma radiation is achieved by a plasma electrochemical circulation device; The plasma electrochemical circulation device comprises: A container for holding a mixed solution; Plasma electrochemical device for the synthesis of anisotropic gold nanoparticles; A monitoring device for monitoring the synthesis of anisotropic gold nanoparticles; The container, the plasma electrochemical device and the monitoring device are connected in series via a pipeline; The mixed solution flows under the driving of the driving device.

5. The preparation method according to claim 4, characterized in that: The plasma electrochemical device comprises a first electrode and a second electrode; When the plasma electrochemical device is working, the first electrode is located in the mixed solution, and the second electrode is located 2-5 mm above the upper surface of the mixed solution; A voltage is applied to the first electrode and the second electrode to break down the gas between the surface of the mixed solution and the second electrode to generate discharge plasma, and radiate the mixed solution overflowing the surface of the plasma electrochemical device.

6. The preparation method according to claim 5, characterized in that: The materials of the first electrode and the second electrode are independently any one of semiconductor materials, metal materials or carbon materials; The second electrode is a tubular electrode or a solid electrode; When the second electrode is a tubular electrode, gas is introduced into the pipe to generate discharge plasma after voltage is applied.

7. The preparation method according to claim 5, characterized in that: The first electrode is a graphite electrode, the second electrode is a tubular tungsten steel electrode, and argon gas is passed through a pipe of the second electrode.

8. The preparation method according to claim 5, characterized in that: The applied voltage is higher than the breakdown voltage of the gas; The irradiation time is 20-40 minutes.

9. The preparation method according to claim 4, characterized in that: The monitoring device includes a cuvette, a light source and an absorption spectrometer; The cuvette is used for collecting mixed solution samples, and the absorption spectrometer is used for detecting absorption spectra.

10. Anisotropic gold nanoparticles are prepared according to the preparation method according to any one of claims 1 to 9.

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