CN111215636B - A kind of preparation method of Ag nanoparticles - Google Patents

Abstract

The invention provides a preparation method of Ag nano-particles. Electricity is provided by a high voltage direct current power supply, a platinum needle is used as an anode, and the AgNO ₃ solution is driven by a peristaltic pump to flow through a buffer bottle, and overflows from the top of a capillary penetrating a graphite carbon rod to overflow. solution as the discharge cathode. When a high enough voltage is applied between the two poles, the overflowing liquid will generate a glow to form a plasma, and the active particles generated by the liquid cathode glow discharge plasma will react with Ag ⁺ in the solution, and the generated Ag nanoparticle turbid liquid will flow along the graphitic carbon rod. The wall flows into the collector. Finally, the turbid liquid is ultrasonically dispersed, centrifuged, washed with distilled water, dried to constant weight, and ground to obtain Ag nanoparticles. The Ag nanoparticles synthesized by the preparation method have uniform structure, good dispersibility and low degree of agglomeration, and have broad application prospects in catalysis, sensors, electrode materials and the like.

Description

A kind of preparation method of Ag nanoparticles

technical field

The invention belongs to the technical field of nanomaterial preparation, and relates to a preparation method of Ag nanoparticles, in particular to a method for directly preparing _Ag nanoparticles from AgNO3 solution by utilizing liquid cathode glow discharge plasma technology.

Background technique

Silver (Ag) nanomaterials have been widely used in surface-enhanced Raman spectroscopy, luminescence and display devices, high-efficiency catalysts, biosensors, and high-performance electrode materials due to their excellent catalytic, optical, and electrical properties. The morphology, distribution and size of silver nanoparticles will affect their properties, so the preparation of various silver nanoparticles with different shapes plays a key role in its application, and this is also a hot spot in nanomaterials research in recent years.

The preparation methods of silver nanoparticles mainly include: reduction method, ultrasonic-assisted method, sol-gel method, microwave method, precipitation method, alcoholysis method, etc. Among them, the preparation of silver nanoparticles by reduction method is a relatively simple and effective method, including chemical reduction method and electrochemical reduction method. Formaldehyde, dimethylacetamide, citrate, etc. are reduced to prepare silver nanoparticles, and stabilizers (PVP, CTAB or silane coupling agents, etc.) are generally added in the process of preparing silver nanoparticles to prevent the agglomeration of nanoparticles, and then Control the particle size generated at the nanoscale. However, the chemical reduction process is cumbersome, and generates waste liquid and waste gas, pollutes the environment, increases costs, and the resulting silver nanoparticles have irregular morphology and wide particle size distribution. The electrochemical principle is to prepare nanomaterials by strong electrolysis under mild conditions. This method has the advantages of simple equipment, simple operation and mild conditions. The disadvantage is that a protective agent must be added, otherwise it is difficult to form silver nanoparticles. For example, Liao Xuehong et al. (Journal of Chemistry from Higher Education Institutions, 2000, 21(12): 1837-1839) synthesized silver nanospheres and dendritic silver nanoparticles of different sizes under the action of ultrasonic waves by adding EDTA protective agent by electrochemical method. . The method has the advantages of short time consumption, simple steps and no pollution.

With the improvement of people's awareness of environmental protection, the green chemical preparation method of silver nanoparticles with simple research methods, controllable morphology, low energy consumption and low pollution has attracted more and more attention. In recent years, there has been a method for preparing silver nanoparticles by liquid _- phase diaphragm plasma method _. The anode liquid diaphragm discharge plasma prepares silver nanoparticles (a method for preparing silver nanoparticles by liquid diaphragm discharge plasma, application number 201710829462.8).

At present, there are many reports on the combination of liquid cathode glow discharge plasma and spectroscopy to detect the content of metal elements in solution (Yu J, et al. SpectrochimicaActa Part B, 2018, 145: 64-70; C. Yang, et al. al. Talanta, 2016, 155: 314-320; Zhang Zhen, et al. Analytical Chemistry, 2013, 41(10):1606-1613), however, there are few reports at home and abroad on the preparation of nanomaterials by this technique.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a simple, fast, green method for synthesizing Ag nanoparticles, namely, using liquid cathode glow discharge plasma to solve the problems of complex preparation process of Ag nanoparticles, high production cost and environmental pollution in the prior art. Ag nanoparticles were directly prepared from a pH=1 silver nitrate solution by bulk method.

In order to achieve the above object, the technical scheme adopted in the present invention is: a preparation method of Ag nanoparticles, a liquid cathode glow discharge plasma generating device is used, electric energy is provided by a high-voltage direct current power supply, and the platinum needle sealed in the quartz tube is The anode, the AgNO ₃ solution with pH=1 flows through the buffer bottle driven by the peristaltic pump, and overflows from the top of the capillary inserted into the graphite carbon rod. The overflowed solution is used as the discharge cathode. When a high enough voltage is applied between the two electrodes, the platinum needle anode and the capillary The liquid overflowing between them generates glow discharge plasma, and the active particles generated by the liquid cathode glow discharge plasma react with Ag ⁺ in the solution to prepare silver nanoparticles.

The preparation method is as follows: take the liquid cathode glow discharge plasma generating device shown in FIG. 1, the generating device includes a solution pool 3, a liquid collector 9 and a three-dimensional moving platform 15, and the bottom of the liquid collector 9 is connected to the product through an infusion tube. The pool 7 is connected; the liquid collector 9 is provided with an end cover 10, the end cover 10 is provided with an exhaust pipe 11 and a graphite pipe 12, the graphite pipe 12 is arranged vertically, and there is a discontinuous gap between the graphite pipe 12 and the end cover , the graphite tube 12 is provided with a capillary 8, the top of the capillary 8 protrudes from the top of the graphite tube 12, the distance between the top surface of the capillary 8 and the top surface of the graphite tube 12 is 2～4mm, and the lower end of the capillary 8 passes through the peristaltic pump hose 5 and The peristaltic pump 4 is communicated, and the peristaltic pump rubber tube 5 is provided with a buffer bottle 6 with a volume of 3 to 7 mL, and the peristaltic pump 4 communicates with the solution pool 3 through the peristaltic pump rubber tube 2; the graphite tube 12 is communicated with the negative electrode of the DC voltage-stabilizing and constant-current power supply 1 A quartz tube 16 is vertically installed on the three-dimensional mobile platform 15, and a platinum needle electrode 14 is sealed in the quartz tube 16. Both ends of the platinum needle electrode 14 extend out of the quartz tube 16, and one end faces the capillary 8, and the other end is connected to the direct current. The positive pole of the voltage-stabilized and constant-current power supply 1 is connected. The diameter of the platinum needle electrode 14 is 0.3-0.7 mm, the length of the platinum needle electrode 14 facing the capillary 8 exposed to the quartz tube 16 is 1 mm, and the inner diameter of the capillary 8 is 0.5-1.2 mm.

During preparation, the three-dimensional moving platform 15 is adjusted so that the distance between the lower end of the platinum needle electrode 14 and the top of the capillary 8 is 1-3 mm; the silver nitrate solution with a pH value of 1 and a molar volume concentration of 0.05-0.15 mol/L is injected into the solution In the pool 3, start the peristaltic pump 4, so that the silver nitrate solution in the solution pool 3 enters the capillary 8 at a constant speed with a flow rate of 1～6mL/min, overflows from the top of the capillary 8, and contacts the lower end of the platinum needle electrode 14; open the direct current Voltage stabilized power supply 1, the voltage between the cathode and anode is controlled to be 480~600V, and the current is 28~58mA; DC voltage stabilized current power supply 1, platinum needle electrode 14 and graphite tube 12 form a closed loop; during the power-on process, from the capillary tube 8 The solution overflowing from the top flows down along the outer wall of the graphite tube 12 after being discharged, and flows into the liquid collector 9 through the discontinuous gap between the graphite tube 12 and the end cover 10, and then enters the product pool 7, and continues to energize for 3~ After 5 hours, a black turbid liquid was obtained, which was ultrasonically dispersed for 10 to 15 minutes, centrifuged at 6000 to 10000 r/min, washed with distilled water for several times to remove Ag ⁺ , and dried under vacuum at 40 to 60 °C to constant weight. , grinding to obtain Ag nanoparticles.

Due to the pulsation of the peristaltic pump 4 itself, the solution overflowed by the capillary 8 fluctuates, causing the generated discharge plasma to fluctuate. The buffer bottle 6 can not only eliminate the pulsation caused by the peristaltic pump 4 to the solution, but also the stable air pressure in the buffer bottle 6 can also The auxiliary peristaltic pump 4 supplies liquid to the capillary 8 at a constant speed to achieve the purpose of improving the discharge stability. The excess liquid flowing out of the capillary 8 acts as a wire for connection with the graphite tube 12 .

Liquid cathode glow discharge is a novel method to generate non-equilibrium low temperature plasma. In the preparation process, the graphite tube is connected to the negative electrode of the power supply, the capillary is embedded in the graphite tube, the tip of the Pt needle is connected to the positive electrode of the power supply, and the overflow of the capillary tube is in contact with the tip of the Pt needle. In an atmospheric pressure air environment, when a certain voltage is applied between the two electrodes, Emits a stable glow, producing UV light, shock waves, high-energy radiation, and highly reactive particles such as HO∙, H∙, O∙, HO ₂ ∙ and H ₂ O ₂ .

The principle of preparation of nanoparticles

1. Current-voltage curve

The DH1722A-6 DC voltage stabilized power supply (voltage 0-1000 V, current 0-500 mA) of Beijing Dahua Radio Company was used to measure the current under different voltages. Figure 2 shows the current-voltage curves of liquid cathode glow discharge plasma drawn by adjusting different voltages when electrolyzing AgNO ₃ electrolyte with pH value of 1 and molar volume concentration of 0.05 mol/L. It can be seen from Figure 2 that the entire discharge process is divided into 4 sections: AB (0~200V) section, the current and voltage are basically linear, and common electrolysis occurs; BC (200~400V) section, as the voltage increases, the current fluctuation decreases; In the CD (400~470V) section, the current is relatively stable, and there are discontinuous sparks; in the DE (over 480V) section, the glow gradually increases with the increase of the voltage. Because the voltage is too high, the energy consumption is large, and the glow is too strong, and the damage to the capillary and the platinum needle electrode is too large. Therefore, the voltage selected in the preparation method of the present invention is 480-600V. Since the voltage range for preparing Ag nanoparticles is 480-600 V, stable glow is generated in this range and stable plasma is formed. Therefore, the current-voltage curve shows that the discharge process in the preparation method of the present invention is not an ordinary electrolysis process, but a Glow discharge process. The insets in Fig. 2 are the glow photos when the voltages are 480V, 550V and 600V respectively. As the voltage increases, the glow increases and the generated plasma volume is larger, which further illustrates that the preparation of Ag nanoparticles by the method of the present invention is in the plasma reactions in the body state.

2. Emission spectrum analysis

The emission spectrum of the liquid cathode glow discharge was measured with an eight-channel high-resolution CCD fiber optic spectrometer (AvaSpec-ULS 2048, AvaSpec, The Netherlands). Figure 3 shows the pH value of Ag nanoparticles prepared at a voltage of 600 V (Example 3). Emission spectra of AgNO ₃ solution with a molar volume concentration of 0.05 mol/L. The spectral lines with wavelengths from 306.0 to 309.0 nm are the transition bands of HO(A ² Ʃ ⁺ →X ² Π) ((1,0) and (0.0)), and the H _β ( 4d ² D→2p ² P ⁰ ) and H _α (3d ² D→2p ² P ⁰ ) lines, excited states O (3p ⁵ P→3s ⁵ S ⁰ ) and ( 3p ³ P→3s ³ S ⁰ ) atomic transition line. This is because the high-energy electrons excited the vaporized water molecules to generate a large amount of HO·, H·, O·. The atomic lines of Na at 589nm and 589.9nm indicate that the electrolyte contains a trace amount of Na ⁺ . The lines generated at 327.9 nm and 338.3 nm correspond to the atomic emission lines of Ag. The above results show that HO·, H·, O· are generated in the solution during the preparation of nano-Ag by liquid cathode glow discharge. Combined with the analysis of current _- voltage curve and emission spectrum, the mechanism of preparation of Ag nanoparticles by liquid cathode glow discharge plasma is put forward. Bombarded by high-energy electrons (e*), it decomposes to generate HO , O , H , e _aq ⁻ etc. The reaction is as follows:

H ₂ O+e*→H + OH + O + H ₂ O + H ₂ + O ₂ + H ₂ O ₂ +e _aq ⁻ +H ₃ O ⁺ (1)

In the presence of Ag ⁺ in solution, it can undergo a reduction reaction with H or e _aq ⁻ :

Ag ⁺ +e _aq ⁻ = Ag (2)

Ag ⁺ +H·=Ag+H ⁺ (3)

By controlling the discharge voltage, the generation speed and concentration of H and e _aq ⁻ in the solution can be controlled, thereby pushing the equations (2) and (3) to the right, and then controlling the morphology of Ag nanoparticles.

The preparation method of the present invention has the following beneficial effects:

1. A plasma-liquid interface is constructed, and a stable glow discharge plasma is formed between the two electrodes to prepare silver nanoparticles, which provides a unique condition for the preparation process.

2. With mild conditions (room temperature, no inert gas protection, low power consumption), simple equipment, easy operation, and controllable process (change parameters such as electrolyte concentration, discharge voltage, discharge time, etc., Ag nanometers with different particle sizes can be obtained. particles), green environmental protection and other advantages.

3. The chemical reagents used are few, the dosage is low, and there is no secondary pollution. It is an environmentally friendly green preparation technology.

4. The product has less impurities, high purity, good dispersibility, and is easy to separate.

Description of drawings

FIG. 1 is a schematic diagram of a liquid cathode glow discharge plasma generating device used in the preparation method of the present invention.

Figure 2 is a current-voltage curve of the liquid cathode glow discharge plasma of the present invention.

Figure 3 is the emission spectrum at 600 V.

Figure 4 shows the XRD patterns of Ag nanoparticles prepared at different voltages (a 480V, 28mA, b 550V, 32mA, c 600V, 58mA).

Figure 5 shows the SEM morphologies of Ag nanorods prepared at different voltages (a480V, 28mA, b550V, 32mA, c600V, 58mA).

Figure 6 is the EDS spectrum of Ag nanoparticles prepared under the condition of 550 V voltage.

Figure 7 is the UV spectrum of Ag nanoparticles prepared under the condition of 550 V voltage.

In Figure 1: 1. DC stabilized power supply, 2. First peristaltic pump hose, 3. Solution pool, 4. Peristaltic pump, 5. Second peristaltic pump hose, 6. Buffer bottle, 7. Product pool, 8 .Capillary tube, 9. Liquid collector, 10. End cap, 11. Exhaust pipe, 12. Graphite tube, 13. Spilled liquid, 14. Platinum needle electrode, 15. Three-dimensional mobile platform, 16. Quartz tube.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

Example 1

The liquid cathode glow discharge plasma generator shown in FIG. 1 was used. Adjust the three-dimensional moving platform 15 so that the distance between the lower end of the platinum needle electrode 14 and the top of the capillary 8 is 1 mm; inject the silver nitrate solution with pH=1 and molar volume concentration of 0.05 mol/L into the solution pool 3, and start the peristaltic pump 4. Make the silver nitrate solution in the solution tank 3 enter the capillary 8 at a constant speed at a flow rate of 1 mL/min, overflow from the top of the capillary 8, and contact the lower end of the platinum needle electrode 14; turn on the DC voltage-stabilized power supply 1 to control the yin and yang The voltage between the electrodes is 480V and the current is 28mA; the DC voltage-stabilized power supply 1, the platinum needle electrode 14 and the graphite tube 12 form a closed loop; during the electrification process, the solution overflowing from the top of the capillary 8 is electrolyzed along the outer wall of the graphite tube 12. It flows downward, and flows into the liquid collector 9 through the discontinuous gap between the graphite tube 12 and the end cap 10, and then enters the product pool 7. After continuing to energize for 5 hours, a black turbid liquid is obtained, and the turbid liquid is ultrasonically dispersed. 10min, centrifuged at 10000r/min, washed with distilled water for several times to remove dissolved Ag ⁺ , vacuum dried to constant weight at 40°C, ground to obtain the product.

Example 2

Take the liquid cathode glow discharge plasma generator shown in FIG. 1 . Adjust the three-dimensional moving platform 15 so that the distance between the lower end of the platinum needle electrode 14 and the top of the capillary 8 is 2 mm; inject the silver nitrate solution with pH=1 and molar volume concentration of 0.10 mol/L into the solution pool 3, and start the peristaltic pump 4. Make the silver nitrate solution in the solution pool 3 enter the capillary 8 at a constant speed with a flow rate of 3.5 mL/min, overflow from the top of the capillary 8, and contact the lower end of the platinum needle electrode 14; turn on the DC voltage-stabilized and constant-current power supply 1, and control the The voltage between the cathode and anode is 550V, and the current is 32mA; the DC voltage-stabilized power supply 1, the platinum needle electrode 14 and the graphite tube 12 form a closed loop; during the electrification process, the solution overflowing from the top of the capillary 8 is electrolyzed along the graphite tube 12. The outer wall flows downward, and flows into the liquid collector 9 through the discontinuous gap between the graphite tube 12 and the end cap 10, and then enters the product pool 7. After continuing to energize for 4 hours, a black turbid liquid is obtained, and the turbid liquid is ultrasonicated. Disperse for 12min, centrifuge at 10000r/min, wash with distilled water for several times to remove dissolved Ag ⁺ , vacuum dry to constant weight at 60°C, grind to obtain the product.

Example 3

Take the liquid cathode glow discharge plasma device shown in Figure 1. Adjust the three-dimensional moving platform 15 so that the distance between the lower end of the platinum needle electrode 14 and the top of the capillary 8 is 3 mm; inject the silver nitrate solution with pH=1 and molar volume concentration of 0.15 mol/L into the solution pool 3, and start the peristaltic pump 4. Make the silver nitrate solution in the solution tank 3 enter the capillary 8 at a constant speed with a flow rate of 6 mL/min, overflow from the top of the capillary 8, and contact the lower end of the platinum needle electrode 14; turn on the DC voltage-stabilized power supply 1 to control the yin and yang The voltage between the electrodes is 600V and the current is 58mA; the DC voltage-stabilized power supply 1, the platinum needle electrode 14 and the graphite tube 12 form a closed loop; during the electrification process, the solution overflowing from the top of the capillary 8 is electrolyzed along the outer wall of the graphite tube 12. It flows downward, and flows into the liquid collector 9 through the discontinuous gap between the graphite tube 12 and the end cap 10, and then enters the product pool 7. After continuing to energize for 3 hours, a black turbid liquid is obtained, and the turbid liquid is ultrasonically dispersed. 15min, centrifuged at 6000r/min, washed with distilled water for several times to remove dissolved Ag ⁺ , vacuum dried to constant weight at 50°C, ground to obtain the product.

The structure and morphology of the products prepared in the examples are characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDS) and ultraviolet spectroscopy (UV-vis).

1. XRD test

The products prepared in Examples 1 to 3 were tested with a Rigaku D/max-2400 X-ray powder diffractometer. Figure 4 shows the XRD patterns of the products prepared under different discharge voltages (where a is Example 1, b is Example 2, and c is Example 3). It can be seen from Figure 4 that at 2 θ = 5 to 90° There are 5 diffraction peaks in the range, located at 38.1°, 44.2°, 64.4°, 77.3°, 81.5° respectively. After comparing with the standard spectrum JCPDS (No. 04-0783) card, all diffraction peak positions and standard card peaks were found The alignment is good, and the five diffraction peaks correspond to the diffraction of (111), (200), (220), (311) and (222) crystal planes of face-centered cubic Ag, respectively. It is indicated that the prepared product is metallic Ag with cubic structure. It can also be seen from Fig. 4 that all diffraction peaks have very obvious broadening, since X-ray diffraction peak broadening is one of the characteristics of nanoparticles, indicating that the prepared products have small particle size. It can also be seen from Fig. 4 that there are no other diffraction peaks in the diffraction spectra of Ag prepared under different voltages, indicating that Ag nanoparticles with higher purity are prepared. According to the Debye-Scherrer formula D = kλ /( β cos θ ) (where k =0.89, λ =0.1542nm, β is the half width), the grain size of Ag nanoparticles calculated at the main peak (111) is 60.23nm ( Fig. 4a), 33.67 nm (Fig. 4b) and 47.62 nm ((Fig. 4c).

2. Scanning electron microscope test

The Ag nanoparticles prepared in Examples 1-3 were scanned with a Quanta2000 scanning electron microscope (SEM) from Czech FEI Company to observe the size and morphology of the samples. Before observation, the samples were vacuum dried at 60°C and then sprayed with gold. The SEM of the samples under different discharge voltages is shown in Figure 5 (where a is Example 1, b is Example 2, and c is Example 3), it can be seen that the prepared Ag nanoparticles are mainly rod-shaped, and the nanoparticles have small agglomeration. , showing nanoscale and uniform distribution.

3. X-ray energy dispersive spectroscopy (EDS) test

Use German Quanta type X-ray energy spectrum (EDS) to test the composition of the Ag nanoparticles obtained in Example 2, and the test results are shown in Figure 6. EDS analysis shows that there are only characteristic peaks of Ag in the sample, and the atomic fraction is 84.07%. In addition, 15.93% of the elements in the EDS analysis are Au, which is caused by gold spraying. It is indicated that the black powdery product prepared by the preparation method of the present invention is pure Ag.

4. UV-vis spectrum test

Ag nanoparticles were analyzed by UV757 UV-Vis spectrophotometer (Shanghai Keheng) in the range of 200-800 nm. FIG. 7 is the ultraviolet spectrum of the sample prepared in Example 2. FIG. A strong absorption peak appears around 480 nm, and two shoulder peaks appear at 268 nm and 300 nm, which are consistent with the UV spectrum of Ag nanoparticles, indicating that the prepared particles are Ag nanoparticles.

Claims (6)

1. a preparation method of Ag nanoparticle, is characterized in that: adopt liquid cathode glow discharge plasma generating device, provide electric energy with high voltage direct current power supply, the platinum needle sealed in quartz tube is anode, _AgNO solution is in peristaltic pump It flows through the buffer bottle and overflows from the top of the capillary inserted into the graphite carbon rod. The overflowing solution is used as the discharge cathode, and a high voltage is applied between the cathode and anode. The liquid overflowing between the platinum needle anode and the capillary generates a glow discharge plasma. Ag nanoparticles are prepared by reacting the active particles generated by the liquid cathode glow discharge plasma with Ag ⁺ in the solution; The liquid cathode glow discharge plasma generating device comprises a solution pool (3), a liquid collector (9) and a three-dimensional moving platform (15). The bottom of the liquid collector (9) is communicated with the product pool (7); An end cover (10) is installed on the device (9), an exhaust pipe (11) and a graphite pipe (12) are arranged on the end cover (10), the graphite pipe (12) is vertically arranged, and the graphite pipe (12) and the end There are discontinuous gaps between the covers, a capillary (8) is arranged in the graphite tube (12), the top of the capillary (8) protrudes from the top of the graphite tube (12), and the lower end of the capillary (8) passes through the peristaltic pump hose (5). The peristaltic pump (4) is communicated, and the peristaltic pump (4) is communicated with the solution pool (3) through the peristaltic pump rubber tube (5); the graphite tube (12) is communicated with the negative electrode of the DC voltage-stabilized power supply (1); the three-dimensional mobile platform ( 15) A quartz tube (16) is vertically installed on the quartz tube (16), a platinum needle electrode (14) is sealed in the quartz tube (16), and both ends of the platinum needle electrode (14) extend out of the quartz tube (16). The other end of the capillary (8) is connected to the positive electrode of the DC voltage-stabilized and constant-current power supply (1); during preparation, the three-dimensional moving platform (15) is adjusted so that the lower end of the platinum needle electrode (14) and the top of the capillary (8) are in contact with each other. The distance is 1 to 3 mm; the silver nitrate solution with pH value of 1 and molar volume concentration of 0.05 to 0.15 mol/L is injected into the solution pool (3), and the peristaltic pump (4) is started to make the nitric acid in the solution pool (3) The silver solution enters the capillary tube (8) at a constant speed, overflows from the top of the capillary tube (8), and contacts the lower end of the platinum needle electrode (14); turn on the DC voltage-stabilized power supply (1), the control voltage is 480-600V, and the current 28 ~ 58mA; during the electrification process, the solution overflowing from the top of the capillary (8) flows down along the outer wall of the graphite tube (12) after electrolysis, and passes through the discontinuous gap between the graphite tube (12) and the end cap (10). It flows into the liquid collector (9), and then enters the product pool (7). After continuous power-on, a cloudy liquid is obtained. The cloudy liquid is ultrasonically dispersed, centrifuged, washed with distilled water, vacuum-dried to constant weight, and ground to obtain Ag nanometers. particle. 2 . The method for preparing Ag nanoparticles according to claim 1 , wherein the distance between the top surface of the capillary tube ( 8 ) and the top surface of the graphite tube ( 12 ) is 2-4 mm. 3 . 3 . The method for preparing Ag nanoparticles according to claim 1 , wherein the volume of the buffer bottle ( 6 ) is 3-7 mL. 4 . 4 . The method for preparing Ag nanoparticles according to claim 1 , wherein the length of the platinum needle electrode ( 14 ) facing the capillary ( 8 ) exposed to the quartz tube ( 16 ) is 1 mm. 5 . 5 . The method for preparing Ag nanoparticles according to claim 1 or 4 , wherein the diameter of the platinum needle electrode ( 14 ) is 0.3-0.7 mm. 6 . 6 . The method for preparing Ag nanoparticles according to claim 1 , wherein the silver nitrate solution in the solution pool ( 3 ) enters the capillary ( 8 ) at a constant speed of 1-6 mL/min. 7 .

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