A method for preparing gold and palladium colloids by plasma-activated alcohol solution

Abstract

This invention belongs to the field of nanomaterial preparation technology and discloses a method for preparing gold and palladium colloids from an alcohol solution using plasma activation. The method includes preparing a mixed solution of water and alcohol, treating it using an atmospheric pressure surface dielectric barrier discharge cold plasma reactor, and adding a metal precursor solution for reaction. This invention uses atmospheric pressure surface dielectric barrier discharge cold plasma with a safe inert gas as the working gas to activate a non-toxic alcohol solution to prepare gold and palladium colloids.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for preparing gold and palladium colloids by plasma-activated alcohol solution. Background Technology

[0002] Noble metal colloids refer to homogeneous mixtures of noble metal nanoparticles with particle sizes ranging from 1 to 100 nm in solution. These noble metal nanoparticles possess unique electronic, optical, quantum size, and chemical reactivity properties, making them important for applications in chemistry, energy, biological detection, targeted drug delivery, and the electronics industry.

[0003] The preparation of noble metal colloids mainly employs chemical reduction and photoreduction methods. While chemical reduction can indeed prepare metal colloids with good stability, it typically requires the use of excessive amounts of toxic and harmful chemical reagents, and the preparation conditions are subject to stringent control. Photoreduction is an effective method for preparing metal colloids, allowing the addition of suitable template agents to produce colloids with specific shapes and crystal faces. However, photoreduction requires high-power xenon lamp irradiation, resulting in high energy consumption and hindering large-scale preparation. Therefore, there is an urgent need to develop a simple, rapid, and environmentally friendly method for preparing noble metal colloids.

[0004] Plasma is the fourth state of matter besides solid, liquid, and gas. It is a non-condensed state system with a certain degree of ionization and macroscopically neutral charge. Cold plasma is a typical non-thermodynamically equilibrium plasma. It is well-suited for the preparation and processing of nanomaterials under mild conditions, and has attracted increasing attention in the field of metal nanoparticle and colloid preparation.

[0005] Chinese patent CN102909388B discloses a method for preparing gold-silver alloy nanoparticles using atmospheric pressure micro-plasma liquid-phase assisted synthesis. This invention uses a stainless steel capillary as the cathode and a platinum electrode as the anode, employing atmospheric pressure DC micro-plasma discharge to prepare gold-silver alloy nanoparticles. However, due to the limited liquid surface area that can be processed by the micro-plasma (approximately 100-500 micrometers in diameter), the generation rate of metal nanoparticles is relatively low. Chinese patent CN105665740A discloses a method for synthesizing colloidal gold nanoparticles in an atmospheric pressure air plasma liquid phase. This method involves placing a plasma device in a mixed solution of chloroauric acid and a reducing agent for a certain period to prepare colloidal gold particles. Because the electrode temperature can reach thousands of degrees Celsius during discharge, the electrode material may melt or oxidize, introducing impurities into the solution and resulting in impure gold nanoparticles. Chinese invention patent ZL2021109370790 discloses a method for preparing graphene oxide-loaded palladium using atmospheric pressure cold plasma in a liquid phase. This invention uses a mixture of argon and hydrogen as the working gas and utilizes atmospheric pressure surface dielectric barrier discharge cold plasma to prepare palladium-loaded graphene oxide in solution. This method does not require any other reducing chemical reagents. While this method offers significant advantages in the preparation of metal nanoparticles, its reliance on hydrogen as the working gas results in relatively poor safety. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for preparing gold and palladium colloids by activating an alcohol solution using atmospheric pressure surface dielectric barrier discharge cold plasma and an inert gas as the working gas. This method does not require the use of flammable and explosive hydrogen gas, nor any other reducing chemical reagents or carriers. Simply adding chloroauric acid or chloropalladic acid to the plasma-activated alcohol solution yields colloidal gold or palladium in a short time, making it a green, rapid, flexible, and safe method.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution: a method for preparing gold and palladium colloids by plasma-activated alcohol solution, comprising the following steps:

[0008] 1. Prepare 2 mL of a mixed solution of water and alcohol;

[0009] 2. In an atmospheric pressure surface dielectric barrier discharge cold plasma reactor, plasma is generated using an inert gas as the working gas to process the mixed solution of water and alcohol described in step 1.

[0010] 3. Add the metal precursor solution to the mixed solution after step 2, mix well, and store at low temperature in the dark to obtain the colloidal product.

[0011] Furthermore, step 1 specifically involves using a pipette to transfer 0.2-1.6 mL of alcohol and 0.4-1.8 mL of water into a glass bottle and shaking well.

[0012] Furthermore, step 2 specifically involves: pouring the mixed solution of water and alcohol obtained in step 1 into an atmospheric pressure surface dielectric barrier discharge cold plasma reactor, adjusting the distance between the solution and the electrode in the reactor, introducing an inert gas as the working gas, stirring the solution with a magnetic stirrer, adjusting the plasma discharge frequency and discharge voltage, and processing the mixed solution through the generated plasma.

[0013] Furthermore, step 3 specifically involves: pouring the mixed solution processed in step 2 into a glass bottle, then adding a metal precursor solution, mixing well, and storing it in the dark at 4-10°C for 10-60 minutes to obtain a colloidal product.

[0014] Furthermore, the alcohol used in step 1 is specifically one of methanol or ethanol.

[0015] Furthermore, the atmospheric pressure surface dielectric barrier discharge cold plasma reactor used in step 2 has a dielectric material of quartz glass or alumina and a metal electrode of silver or tungsten.

[0016] Furthermore, in step 2, the distance between the solution and the electrode in the reactor is 2-5 mm, and the depth of the mixed solution is 4-10 mm.

[0017] Furthermore, the inert gas introduced in step 2 is one of Ar, N2, or He, and the total gas flow rate is 20-200 mL / min. -1 .

[0018] Furthermore, in step 2, the rotation speed of the magnetic stirrer is 200-800 r / min. -1 .

[0019] Furthermore, in step 2, the plasma discharge frequency is 50Hz-100kHz, the discharge voltage is a sinusoidal high voltage with a peak-to-peak value of 4.0-30.0kV, and the treatment time for the alcohol solution is 3-12min.

[0020] Furthermore, the metal precursor solutions added in step 3 are chloroauric acid and chloropalladium acid, respectively, and the concentration of the added chloroauric acid is 20 mM·L. -1 The concentration of added chloropalladium acid was 260 mM·L. -1 The final concentration of chloroauric acid or chloropalladium acid in the mixed solution after addition is 0.01-0.50 mM·L. -1 .

[0021] The advantages of this invention compared to existing technologies are as follows: It employs atmospheric pressure surface dielectric barrier discharge cold plasma, using a safe inert gas as the working gas, to activate a non-toxic alcohol solution to prepare gold and palladium colloids. This method does not require hydrogen gas, nor any other toxic or harmful reducing chemical reagents or carriers. Simply adding chloroauric acid or chloropalladic acid solution to the plasma-activated alcohol solution yields colloidal gold or palladium in a short time. The plasma-activated alcohol solution can be stored and used, making production safe, convenient, green, and rapid. This provides a flexible and safe new method for the preparation of gold and palladium colloids. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 UV-vis absorption spectrum and sample photograph of chloroauric acid reduced by aqueous solution activated by argon plasma;

[0024] Figure 2 UV-vis absorption spectrum and sample photograph of chloroauric acid reduced in alcohol solution by argon plasma activation;

[0025] Figure 3 UV-vis absorption spectra and sample photographs of ethanol solution reduced with chloropalladic acid and palladium nitrate by argon plasma activation;

[0026] Figure 4 UV-vis absorption spectrum and sample photograph of silver nitrate reduced by ethanol solution activated by argon plasma;

[0027] Figure 5 UV-vis absorption spectrum and sample photograph of chloroplatinic acid reduced by ethanol solution activated by argon plasma. Detailed Implementation

[0028] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0029] Example 1

[0030] Argon plasma activated aqueous solution for reduction of chloroauric acid:

[0031] The reduction of chloroauric acid by argon plasma activation of aqueous solution is performed as follows: First, transfer 2 mL of water into a quartz reactor (3 cm in diameter, 4 mm deep) using a pipette. Adjust the height of the quartz reactor so that the liquid surface is 2 mm from the electrode. After sealing the device, connect the circuit and purge with Ar gas for 5 min at a flow rate of 100 mL / min. -1 Set the magnetic stirrer speed to 500 rpm.-1 The discharge frequency was adjusted to 10.4 kHz using an oscilloscope, the peak-to-peak value of the sinusoidal discharge voltage was 9.0 kV, and the discharge time was 7 minutes. After the discharge was completed, the power supply and gas circuit were turned off. The treated aqueous solution was poured into a 5 mL graduated cylinder, and an appropriate amount of chloroauric acid of a certain concentration was added to ensure that the solution volume was 2 mL and the chloroauric acid concentration was 0.25 mM·L⁻¹. -1 Then store in a cool, dark place.

[0032] Example 2

[0033] Argon plasma activated alcohol solution for reduction of chloroauric acid:

[0034] The reduction of chloroauric acid in an alcohol solution using argon plasma activation is performed as follows: First, transfer 1 mL of water and 1 mL of methanol or ethanol into a quartz reactor (3 cm in diameter, 4 mm deep) using a pipette. Adjust the height of the quartz reactor so that the liquid surface is 2 mm from the electrode. After sealing the device, connect the circuit and purge with Ar gas for 5 min at a flow rate of 100 mL / min. -1 Set the magnetic stirrer speed to 500 rpm. -1 The discharge frequency was adjusted to 10.4 kHz using an oscilloscope, the peak-to-peak value of the sinusoidal discharge voltage was 9.0 kV, and the discharge time was 7 minutes. After the discharge was completed, the power supply and gas circuit were turned off. The treated alcohol solution was poured into a 5 mL graduated cylinder, and an appropriate amount of chloroauric acid of a certain concentration, as well as methanol or ethanol, were added to ensure that the solution volume was 2 mL and the chloroauric acid concentration was 0.25 mM·L⁻¹. -1 Then store in a cool, dark place.

[0035] Example 3

[0036] Argon plasma activated ethanol solution for the reduction of chloropalladium acid and palladium nitrate:

[0037] Argon plasma activated ethanol solution for the reduction of chloropalladic acid and palladium nitrate is performed using the following steps: First, transfer 1 mL of water and 1 mL of ethanol into a quartz reactor (3 cm in diameter, 4 mm deep) using a pipette. Adjust the height of the quartz reactor so that the liquid surface is 2 mm from the electrode. After sealing the device, connect the circuit and purge with Ar gas for 5 minutes at a flow rate of 100 mL / min. -1 Set the magnetic stirrer speed to 500 rpm. -1 The discharge frequency was adjusted to 10.4 kHz using an oscilloscope, the peak-to-peak value of the sinusoidal discharge voltage was 9.0 kV, and the discharge time was 7 minutes. After the discharge was completed, the power supply and gas circuit were turned off. The treated ethanol solution was poured into a 5 mL graduated cylinder, and an appropriate amount of palladium chloroacetic acid or palladium nitrate solution of a certain concentration and ethanol were added to ensure that the solution volume was 2 mL and the concentration of palladium chloroacetic acid or palladium nitrate was 0.25 mM·L⁻¹. -1 Then store in a cool, dark place.

[0038] Example 4

[0039] Argon plasma activation of ethanol solution to reduce silver nitrate:

[0040] The reduction of silver nitrate by argon plasma activation of ethanol solution is similar to that in Example 3, except that the chloropalladium acid or palladium nitrate solution is replaced with silver nitrate solution.

[0041] Example 5

[0042] Argon plasma activation of ethanol solution for reduction of chloroplatinic acid:

[0043] Argon plasma activation of ethanol solution to reduce chloroplatinic acid follows a similar procedure to Example 3, except that the chloropalladium acid or palladium nitrate solution is replaced with chloroplatinic acid solution.

[0044] Analysis of UV-vis absorption spectra and sample photographs of chloroauric acid reduced by aqueous solution activated by argon plasma:

[0045] like Figure 1 As can be seen, after adding chloroauric acid to the argon plasma-activated aqueous solution, the solution showed no significant color change or UV-vis absorption spectrum change after 24 hours. No gold plasmon resonance absorption peak was observed at 540 nm, indicating that colloidal gold nanoparticles did not appear in the solution. This demonstrates that the commonly accepted reduction by hydrated electrons cannot exist in a simply activated aqueous solution, and therefore, it is impossible to reduce noble metal precursors to prepare noble metal colloids.

[0046] Analysis of UV-vis absorption spectra and sample photographs of chloroauric acid reduced in alcohol solution by argon plasma activation:

[0047] like Figure 2 As can be seen, after plasma-activated methanol and ethanol solutions were added with chloroauric acid, the colors of both solutions changed significantly within 10 minutes. A clear plasmon resonance absorption peak for gold nanoparticles also appeared in the UV-Vis absorption spectra, indicating that plasma-activated alcohol solutions can reduce chloroauric acid to produce gold colloidal nanoparticles. This demonstrates that plasma-activated alcohol solutions can generate active species for reducing noble metal precursors. Furthermore, it was observed that plasma-activated ethanol solutions reduced chloroauric acid at a faster rate.

[0048] Analysis of UV-vis absorption spectra and sample photographs of argon plasma-activated ethanol solution reduction of chloropalladic acid and palladium nitrate:

[0049] like Figure 3As can be seen, after 10 minutes of plasma-activated ethanol solution being added to chloropalladium acid solution, a significant color change and a marked enhancement in the UV-Vis absorption spectrum were observed, indicating that plasma-activated ethanol solution can reduce chloropalladium acid to produce palladium colloidal nanoparticles. However, after adding palladium nitrate solution to plasma-activated ethanol solution, no significant color change or UV-Vis absorption spectrum change was observed, indicating that plasma-activated ethanol solution cannot reduce palladium nitrate to produce palladium colloidal nanoparticles. This suggests that nitrate ions have a quenching effect on the reducing active species produced by plasma-activated ethanol solution.

[0050] Analysis of UV-vis absorption spectra and sample photographs of silver nitrate reduced by ethanol solution activated by argon plasma:

[0051] like Figure 4 As can be seen, the color of the plasma-activated ethanol solution did not change significantly after the addition of silver nitrate solution, and the UV-vis absorption spectrum also showed no significant change. No plasmon resonance absorption peak of silver was observed at 420 nm, indicating that the plasma-activated ethanol solution could not reduce silver nitrate to produce silver colloidal nanoparticles. This further demonstrates that nitrate ions have a quenching effect on the reducing active species produced by the plasma-activated ethanol solution.

[0052] UV-vis absorption spectrum and sample photograph of chloroplatinic acid reduced by ethanol solution activated by argon plasma:

[0053] like Figure 5 As can be seen, after adding chloroplatinic acid solution to plasma-activated ethanol solution, the solution color and UV-vis absorption spectrum showed no significant changes after 10 min and 1 h, respectively. No absorption band for platinum nanoparticles was generated in the visible light region, indicating that plasma-activated ethanol solution cannot reduce chloroplatinic acid to produce platinum colloidal nanoparticles. This is due to the presence of PtCl6. 2- The reduction to Pt nanoparticles requires a two-step reaction; the active species in the activated ethanol solution cannot effectively reduce PtCl6. 2- .

[0054] in conclusion:

[0055] In summary, argon plasma-activated aqueous solutions cannot reduce noble metal precursors. Argon plasma-activated ethanol solutions exhibit stronger reducing power for chloroauric acid and chloropalladium acid than plasma-activated methanol solutions. Due to the quenching effect of nitrate ions, plasma-activated alcohol solutions cannot reduce palladium nitrate and silver nitrate precursors, thus preventing the preparation of palladium and silver colloidal nanoparticles. Furthermore, since the reduction of metal ions in chloroplatinic acid involves a two-step reaction, plasma-activated alcohol solutions cannot effectively reduce them to prepare platinum colloidal nanoparticles.

[0056] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing gold and palladium colloids by plasma-activated alcohol solution, characterized in that the steps include... include: S1. Prepare 2 mL of a mixed solution of water and alcohol, wherein the alcohol is specifically one of methanol or ethanol; S2. In an atmospheric pressure surface dielectric barrier discharge cold plasma reactor, plasma is generated using an inert gas as the working gas to process the mixed solution of water and alcohol described in step S1. S3. Add the metal precursor solution to the mixed solution after step S2, mix well, and store at low temperature in the dark to obtain a colloidal product. The metal precursor solutions are chloroauric acid and chloropalladium acid, and the concentration of the added chloroauric acid is 20 mM·L. -1 The concentration of added chloropalladium acid was 260 mM·L. -1 The final concentration of chloroauric acid or chloropalladium acid in the mixed solution after addition is 0.01-0.50 mM∙L. -1 .

2. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 1, characterized in that, Step S1 specifically involves using a pipette to transfer 0.2-1.6 mL of alcohol and 0.4-1.8 mL of water into a glass bottle and shaking well.

3. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 1, characterized in that, Step S2 specifically involves: pouring the mixed solution of water and alcohol obtained in step S1 into an atmospheric pressure surface dielectric barrier discharge cold plasma reactor, adjusting the distance between the solution and the electrode in the reactor, introducing an inert gas as the working gas, stirring the solution with a magnetic stirrer, adjusting the plasma discharge frequency and discharge voltage, and processing the mixed solution through the generated plasma.

4. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 1, characterized in that, Step S3 specifically involves: pouring the mixed solution processed in step S2 into a glass bottle, then adding the metal precursor solution, mixing well, and storing it in the dark at 4-10°C for 10-60 minutes to obtain the colloidal product.

5. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 1, characterized in that, The atmospheric pressure surface dielectric barrier discharge cold plasma reactor used in step S2 has a dielectric material of quartz glass or alumina and a metal electrode of silver or tungsten.

6. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 3, characterized in that, In step S2, the distance between the solution and the electrode in the reactor is 2-5 mm, and the depth of the mixed solution is 4-10 mm.

7. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 3, characterized in that, The inert gas introduced into the reactor in step S2 is one of Ar, N2, or He, with a total gas flow rate of 20-200 mL·min. -1 .

8. The method for preparing gold and palladium colloids by plasma-activated alcohol solution according to claim 3, characterized in that, In step S2, the rotation speed of the magnetic stirrer is 200-800 r·min. -1 The plasma discharge frequency is 50 Hz-100kHz, the discharge voltage is sinusoidal high voltage with a peak-to-peak value of 4.0-30.0 kV, and the treatment time for the alcohol solution is 3-12 min.

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