CN110405223B - Preparation method of high-purity size-controllable nano gold particles - Google Patents
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Abstract
A preparation method of high-purity gold nanoparticles with controllable sizes belongs to the field of metal materials. The preparation steps comprise four steps of target material smelting, nanometer seed preparation through laser ablation, nanometer particle growth through chemical inoculation and centrifugal separation. Wherein the growth of the chemically inoculated nanoparticles is realized by combining a seed growth method with a co-reduction technology using sodium citrate as a reducing agent to ensure the monodispersion of gold particles and control the formation of gold nanoparticles of a certain size; for large size gold particles, a multi-step particle growth process must be used. The centrifugal separation is to generate a centrifugal force field in the rotor through the high-speed rotation of the rotor, and the light and heavy components have difference in radial pressure distribution of the rotor in the centrifugal force field to separate out high-purity gold powder. The method has the advantages of ingenious design, simplicity, reliability, firmness, durability and low cost, and can be used for preparing high-purity gold powder products with a certain scale.
Description
Technical Field
The invention is applied to the key technical field of production of noble metal pasty materials, and particularly relates to the manufacturing of a gold coating film on the surface of a precision instrument.
Background
The noble metal paste material is used as an optical coating product with special application, and a gold film which is firmly adhered, has no stain, has golden yellow surface and excellent conductivity can be formed on the cylindrical surface of the optical glass fiber panel after sintering. The gold paste is coated on the cylindrical surface of an optical glass fiber panel, and after sintering, the finish degree reaches more than 12 grades, so that the gold paste is applied to different fields.
Besides being widely applied to the decoration of porcelain, fine pottery, glass and other products, the gold paste is also widely applied to the conductive layer, the reflection and protection film and the like in the aspects of buildings, optics, electric appliances and the like. With the increasing development of the electronic industry, metal organic compounds are used as a new technology for thick film conductor and resistor paste. The slurry is added with photosensitizer, and the exposure technology is adopted, so that the slurry can be used for manufacturing products such as a heat reflection head with any pattern, a circuit for an image sensor and the like. A small amount of base metal resinate is added into the common gold slurry to form a novel structure with activity, so that the adhesion is improved, and the compactness of a film layer is improved.
In order to prevent the electrode from generating the discharge phenomenon, the surface roughness Ra of the sintered gold film is required to be less than or equal to 0.1 mu m, stains and black spots are not allowed to be formed on the gold paste sintered film, the optical glass fiber panel has good adhesive force, and the gold paste is weak in acid and weak in alkali, so that the requirements on the preparation process of the nano gold particles are particularly important.
Disclosure of Invention
In order to solve the problems of preparation of high-purity nano gold particles and application of gold paste in night vision devices and the like, the invention aims to obtain the required nano gold particles by strictly controlling the purity of gold and the size of the nano gold particles through laser ablation and chemical inoculation growth, and finally prepare the gold paste by fully stirring the nano gold particles with an organic solvent so as to meet the requirements of military industry on high purity and high density of gold powder.
A preparation method of high-purity gold nanoparticles with controllable sizes is characterized by comprising the following specific steps:
(1) smelting a target material: vacuum smelting is carried out on the gold target material, one-way sealing of a vacuum door is changed into two-way sealing, the vacuum door is lined with a heat insulation sealing material, and a stainless steel wire mesh is added to the top of the mist eliminator;
(2) preparing nano seeds by laser ablation;
(3) and (3) chemically inoculating nanoparticles for growth: by combining a seed growth method with a co-reduction technology using sodium citrate as a reducing agent, monodispersion of gold particles is ensured and formation of gold nanoparticles of a certain size is controlled; for large size gold particles, a multi-step particle growth process must be used;
(4) centrifugal separation: through the high-speed rotation of the rotor, a centrifugal force field is generated in the rotor, and the light and heavy components have difference in distribution along the radial pressure intensity of the rotor in the centrifugal force field, so that high-purity gold powder is separated.
The preparation method of the high-purity gold nanoparticles with controllable sizes comprises the following specific preparation steps:
(1) smelting of target material
Before smelting, firstly, oil pumping in a vacuum pump is updated, and then the metal auxiliary material is baked in a baking furnace at the temperature of 380-420 ℃ for 25-35min to remove moisture; the reading of the vacuum degree is less than 0.01Pa, the smelting temperature is 1150-1250 ℃, and the smelting time is 10-12 h; smelting for 5-7 times to finally obtain a pure gold target material with the purity of 99.999%;
(2) laser ablation preparation of nano-seed
Firstly, treating the target surface of Au by using 500-granularity carborundum paper to remove surface defects; the target material is cleaned in an ultrasonic bath of acetone and ethanol for 18-12 minutes and then rinsed with deionized water to eliminate any contaminants present; place the cleaned target at the bottom of a pyrex glass container filled with 70 vol% ethanol, using pulsed Nd: YAG laser as radiation source, fundamental wave wavelength: 1064nm; pulse duration 8ns; repetition rate: 10 Hz; the laser beam is focused on the surface of the Au target by a lens with the focal length of 90-110mm to obtain the laser energy density of 20J/cm 2; performing ablation at room temperature for 218-22min to obtain pure Au colloidal solution with average particle size of 20 nm;
(3) chemical seeding nanoparticle growth
The gold particles after laser ablation are chemically inoculated and grown to meet the size requirement; metal-based reduction converts metal ions into neutral atoms, the low solubility of these free atoms induces them to rapidly nucleate into small metal clusters, and the remaining neutral atoms then grow on the existing particles; gold particle growth is formed by reducing chloroauric acid with sodium citrate in water; the size of the gold particles was controlled by varying the ratio of Au to citrate during synthesis; pure Au particles have been achieved by using a seed growth method, where small monodisperse nanoparticles are first formed and then used as seeds for growing larger gold particles; during the growth step, the formation of new seeds is prevented by fine control of the growth conditions and selection of a suitable reducing agent.
(4) And centrifugal separation
And (3) using a centrifugal machine, setting the rotating speed to 1800 plus 2200 revolutions per minute, operating for 13-17 minutes, centrifuging at a high speed, and filtering out the finally prepared high-purity gold powder.
Further, the fine control growth conditions of step (3) are: in the growth process, a control method of short time, low concentration, multiple frequency and staging is adopted, the shaking time of each time is controlled to be not more than 1 minute, the standing time is not more than 10 minutes, the chloroauric acid solution and the reducing agent solution are controlled to be not more than 0.02mol/L, and the gold nanoparticles are grown in stages by taking care of adding multiple times with low concentration when the solution is added; in this preparation, the reducing agent is selected as: ascorbic acid, sodium bromide and sodium citrate.
Description of specific steps:
(1) smelting a target material: the gold target material is subjected to vacuum smelting, and only partial improvement is performed on a vacuum furnace: the installation mode of the vacuum valve is improved, one-time sealing of the vacuum door is changed into two-time sealing, the lining heat-insulation sealing material of the vacuum door is modified, the graphite rod conducting seat material is modified, and the like. Because the smelting chamber has larger space, uniform heat distribution and easy temperature adjustment, the continuous distillation, collection and extraction of the gold are smooth. The spontaneous combustion and volatilization of the smelting slag in the volatilization cooling chamber are smooth, the absorption effect of the absorption tower is good, the initial effect of the multi-gear foam catcher is poor, and then the stainless steel wire mesh is added at the top of the foam catcher, so that the good effect is achieved, and the smelting slag is washed by water regularly. Through multiple times of smelting, the purity of the smelted gold target material reaches 99.999 percent.
(2) Preparing nano seeds by laser ablation: at present, there are many methods for preparing gold nano-materials, such as solution method, photochemical method, electrolytic method, chemical vapor deposition method, direct current sputtering method, particle beam bombardment method, etc., and the methods can be roughly classified into chemical method and physical method according to the principle. In the chemical method, gold nano-crystalline particles mostly exist in a solution or colloid environment, in order to prevent clustering of the crystalline particles and increase the stability of the crystalline particles, chemical substances such as a dispersing agent, a passivating agent, a stabilizing agent and the like are often required to be added, and the substances not only can cause the purity reduction and the performance reduction of the nano-crystalline particles, but also can cause a certain degree of environmental pollution; meanwhile, in the process of forming the gold nano-film, the thickness and uniformity are difficult to control. The laser ablation technology is adopted to prepare the gold nano material, which belongs to a physical method and can effectively avoid the problems. Compared with direct current sputtering and particle beam bombardment in a physical method, the laser ablation technology has the advantages of high heating speed and high efficiency due to high laser energy, and can be used for preparing refractory substances such as metal, ceramic and the like; in addition, the laser ablation technology can also be used for researching the morphology, the structure and the growth kinetic process of the nano crystal grains from different angles by changing experimental conditions such as laser wavelength, pulse width and frequency, laser energy, environmental gas types and pressure, target-substrate spacing, environmental temperature and the like.
(3) And (3) chemically inoculating nanoparticles for growth: by combining the seed growth method with a co-reduction technique using sodium citrate as a reducing agent, monodispersion of gold particles and formation of gold nanoparticles of a certain size can be ensured. The proportion of the seed Au-citrate must be very carefully controlled, since the reduction at high temperatures causes undesirable nucleation. If the seed concentration is high, the metal monomer is more likely to grow on the existing seed rather than forming a new nucleus. Therefore, it is preferable to use a high seed-to-metal ion concentration. However, this limits the final size of the particles. For large size gold particles, a multi-step particle growth process must be used.
(4) Centrifugal separation: through the high-speed rotation of the rotor, a centrifugal force field is generated in the rotor, and the light and heavy components have difference in distribution along the radial pressure intensity of the rotor in the centrifugal force field, so that high-purity gold powder is separated.
Our method relies on continued growth on small Au seeds, producing monodisperse gold nanoparticles to size requirements. Gold as a seed, they are more stable and easier to produce, with small Au seeds present in the center, having no significant effect on the optical properties of particles larger than 50nm in diameter. Even at 30nm, the theoretical plasma peak position shifts only slightly, but the peak is wider. The resulting gold nanoparticles can be used as seeds for subsequent gold growth, and the process repeated until the desired size is reached.
The method designed by the invention has the advantages of ingenious design, simplicity, reliability, firmness, durability and low cost, and can be used for preparing high-purity gold powder products with a certain scale
Detailed Description
Example one:
1. smelting of target material
Before smelting, firstly, the pump oil in the vacuum pump needs to be updated, because old pump oil can influence the degassing effect, the diffusion pump needs to be preheated for 50min, and then auxiliary materials such as metal and the like need to be baked for 30min in a baking furnace at 400 ℃ to remove moisture. Feeding 0.5kg of materials into each furnace, reading the vacuum degree of less than 0.01Pa, smelting at about 1200 ℃ and smelting time of 12 h; the smelting times are 6 times, and the pure gold target with the purity of 99.999 percent is finally obtained.
2. Preparation of nano-seed by laser ablation
First, the target surface of Au was treated with emery paper (having a grain size of 500) to remove surface defects. The target was cleaned in an ultrasonic bath of acetone and ethanol for 10 minutes and then rinsed with deionized water to remove any contaminants present. The cleaned target was placed at the bottom of a pyrex glass container (volume 15mL) filled with 70 vol% ethanol, using a pulsed Nd: YAG laser (fundamental wave wavelength: 1064nm; pulse duration 8ns; repetition rate: 10Hz) was used as the radiation source. The laser beam was focused by a lens with a focal length of 100mm on the surface of the Au target to obtain a laser energy density of about 20J/cm 2. The ablation process was carried out at room temperature for 20min to obtain pure Au colloidal solution with an average particle size of 20 nm.
3. Chemical seeding nanoparticle growth
The size requirement is achieved by chemically inoculating and growing the gold particles after laser ablation. Metal-based reduction converts metal ions to neutral atoms. The low solubility of these free atoms induces their rapid nucleation into small metal clusters, and the remaining neutral atoms then grow on the existing particles. Gold particle growth is formed by reducing chloroauric acid with sodium citrate in water. In this method, the size of the gold particles can be controlled by varying the ratio of Au to citrate during synthesis. For small sizes, the process may produce gold particles with a coefficient of variation (defined as the standard deviation of the size distribution divided by the mean size), but with a content below 10%, which corresponds to excellent monodispersity. However, when large (>40nm) gold particles are produced, the dispersion of size and shape is worse.
The most critical aspect of the synthesis of monodisperse gold nanoparticles is the temporal separation of nucleation and growth steps during formation. Pure Au particles have been achieved by using a seed growth method, where small monodisperse nanoparticles are first formed and then they are used as seeds for growing larger gold particles. It is important to prevent the formation of new seeds during the growth step. This is achieved by fine control of the growth conditions and selection of a suitable reducing agent. The presence of reducing ions at the metal surface at low temperatures is selected to prevent new nucleation, and this seed growth method has been successfully used to synthesize large and size-controlled Au particles.
4. Centrifugal separation
And (3) using a centrifugal machine, setting the rotating speed to 2000 revolutions per minute, operating for 15 minutes, centrifuging at a high speed, and filtering to obtain the finally prepared high-purity gold powder.
Example two:
1. smelting of target material
Before smelting, firstly, the pump oil in the vacuum pump needs to be updated, because old pump oil can influence the degassing effect, the diffusion pump needs to be preheated for 50min, and then, auxiliary materials such as metal and the like need to be baked for 25min in a baking furnace at 380 ℃ to remove moisture. Feeding 0.2kg of materials into each furnace, reading the vacuum degree of less than 0.01Pa, smelting at about 1200 ℃ and smelting time of 10 hours; the smelting times are 5 times, and the pure gold target with the purity of 99.999 percent is finally obtained.
2. Preparation of nano-seed by laser ablation
First, the target surface of Au was treated with emery paper (having a grain size of 500) to remove surface defects. The target was cleaned in an ultrasonic bath of acetone and ethanol for 15 minutes and then rinsed with deionized water to remove any contaminants present. The cleaned target was placed at the bottom of a pyrex glass container (volume 15mL) filled with 70 vol% ethanol, using a pulsed Nd: YAG laser (fundamental wave wavelength: 1064nm; pulse duration 8ns; repetition rate: 10Hz) was used as the radiation source. The laser beam was focused by a lens with a focal length of 100mm on the surface of the Au target to obtain a laser energy density of about 20J/cm 2. The ablation process was carried out at room temperature for 18min to obtain pure Au colloidal solution with an average particle size of 25 nm.
3. Chemical seeding nanoparticle growth
The size requirement is achieved by chemically inoculating and growing the gold particles after laser ablation. Metal-based reduction converts metal ions to neutral atoms. The low solubility of these free atoms induces their rapid nucleation into small metal clusters, and the remaining neutral atoms then grow on the existing particles. Gold particle growth is formed by reduction of chloroauric acid with sodium bromide in water. In this method, the size of the gold particles can be controlled by varying the ratio of Au to sodium bromide during synthesis. For small sizes, the process may produce gold particles with a coefficient of variation (defined as the standard deviation of the size distribution divided by the mean size), but with a content below 10%, which corresponds to excellent monodispersity. However, when large (>40nm) gold particles are produced, the dispersion of size and shape is worse.
The most critical aspect of the synthesis of monodisperse gold nanoparticles is the temporal separation of nucleation and growth steps during formation. Pure Au particles have been achieved by using a seed growth method, where small monodisperse nanoparticles are first formed and then they are used as seeds for growing larger gold particles. It is important to prevent the formation of new seeds during the growth step. This is achieved by fine control of the growth conditions and selection of a suitable reducing agent. The presence of reducing ions at the metal surface at low temperatures is selected to prevent new nucleation, and this seed growth method has been successfully used to synthesize large and size-controlled Au particles.
4. Centrifugal separation
And (3) using a centrifugal machine, setting the rotating speed to 1800 revolutions per minute, operating for 17 minutes, centrifuging at a high speed, and filtering out the finally prepared high-purity gold powder.
Example three:
1. smelting of target material
Before smelting, firstly, the pump oil in the vacuum pump needs to be updated, because old pump oil can influence the degassing effect, the diffusion pump needs to be preheated for 50min, and then, auxiliary materials such as metal and the like need to be baked for 35min in a baking furnace at the temperature of 420 ℃ to remove moisture. Feeding 0.7kg of materials into each furnace, reading the vacuum degree of less than 0.01Pa, smelting at about 1200 ℃ and smelting time of 12 h; the smelting times are 7 times, and the pure gold target with the purity of 99.999 percent is finally obtained.
2. Preparation of nano-seed by laser ablation
First, the target surface of Au was treated with emery paper (having a grain size of 500) to remove surface defects. The target was cleaned in an ultrasonic bath of acetone and ethanol for 20 minutes and then rinsed with deionized water to remove any contaminants present. The cleaned target was placed at the bottom of a pyrex glass container (volume 15mL) filled with 70 vol% ethanol, using a pulsed Nd: YAG laser (fundamental wave wavelength: 1064nm; pulse duration 8ns; repetition rate: 10Hz) was used as the radiation source. The laser beam was focused by a lens with a focal length of 100mm on the surface of the Au target to obtain a laser energy density of about 20J/cm 2. The ablation process was carried out at room temperature for 202min to obtain pure Au colloidal solution with an average particle size of 15 nm.
3. Chemical seeding nanoparticle growth
The size requirement is achieved by chemically inoculating and growing the gold particles after laser ablation. Metal-based reduction converts metal ions to neutral atoms. The low solubility of these free atoms induces their rapid nucleation into small metal clusters, and the remaining neutral atoms then grow on the existing particles. Gold particle growth is formed by the reduction of chloroauric acid with ascorbic acid in water. In this method, the size of the gold particles can be controlled by varying the ratio of Au to ascorbic acid during synthesis. For small sizes, the process may produce gold particles with a coefficient of variation (defined as the standard deviation of the size distribution divided by the mean size), but with a content below 10%, which corresponds to excellent monodispersity. However, when large (>40nm) gold particles are produced, the dispersion of size and shape is worse.
The most critical aspect of the synthesis of monodisperse gold nanoparticles is the temporal separation of nucleation and growth steps during formation. Pure Au particles have been achieved by using a seed growth method, where small monodisperse nanoparticles are first formed and then they are used as seeds for growing larger gold particles. It is important to prevent the formation of new seeds during the growth step. This is achieved by fine control of the growth conditions and selection of a suitable reducing agent. The presence of reducing ions at the metal surface at low temperatures is selected to prevent new nucleation, and this seed growth method has been successfully used to synthesize large and size-controlled Au particles.
4. Centrifugal separation
And (3) using a centrifugal machine, setting the rotating speed to 2500 revolutions per minute, operating for 15 minutes, centrifuging at a high speed, and filtering to obtain the finally prepared high-purity gold powder.
Claims (2)
1. A preparation method of high-purity gold nanoparticles with controllable sizes is characterized by comprising the following preparation steps:
(1) smelting a target material: vacuum smelting is carried out on the gold target material, one-way sealing of a vacuum door is changed into two-way sealing, the vacuum door is lined with a heat insulation sealing material, and a stainless steel wire mesh is added to the top of the mist eliminator; before smelting, firstly, oil pumping in a vacuum pump is updated, and then the metal auxiliary material is baked in a baking furnace at the temperature of 380-420 ℃ for 25-35min to remove moisture; the reading of the vacuum degree is less than 0.01Pa, the smelting temperature is 1150-1250 ℃, and the smelting time is 10-12 h; smelting for 5-7 times to finally obtain a pure gold target material with the purity of 99.999%;
(2) preparing nano seeds by laser ablation; firstly, treating the target surface of Au by using 500-granularity carborundum paper to remove surface defects; the target material is put in an ultrasonic bath of acetone and ethanol for cleaning for 15-20 minutes, and then is washed by deionized water to eliminate any existing pollutants; place the cleaned target at the bottom of a pyrex glass container filled with 70 vol% ethanol, using pulsed Nd: YAG laser as radiation source, fundamental wave wavelength: 1064nm, pulse duration 8ns, repetition rate: 10 Hz; the laser beam is focused on the surface of the Au target by a lens with a focal length of 90-110mm to obtain 20J/cm2Laser energy density of (2); performing ablation at room temperature for 18-22min to obtain pure Au colloidal solution with average particle diameter of 20 nm;
(3) and (3) chemically inoculating nanoparticles for growth: by combining a seed growth method with a co-reduction technology using sodium citrate as a reducing agent, monodispersion of gold particles is ensured and formation of gold nanoparticles of a certain size is controlled; for large size gold particles, a multi-step particle growth process must be used; the gold particles after laser ablation are chemically inoculated and grown to meet the size requirement; metal-based reduction converts metal ions into neutral atoms, the low solubility of these free atoms induces them to rapidly nucleate into small metal clusters, and the remaining neutral atoms then grow on the existing particles; gold particle growth is formed by reducing chloroauric acid with sodium citrate in water; the size of the gold particles was controlled by varying the ratio of Au to citrate during synthesis; pure Au particles have been achieved by using a seed growth method, where small monodisperse nanoparticles are first formed and then used as seeds for growing larger gold particles; during the growth step, the formation of new seeds is prevented by fine control of the growth conditions and selection of suitable reducing agents;
(4) centrifugal separation: through the high-speed rotation of the rotor, a centrifugal force field is generated in the rotor, and the light and heavy components have difference in distribution along the radial pressure intensity of the rotor in the centrifugal force field, so that high-purity gold powder is separated; and (3) using a centrifugal machine, setting the rotating speed to 1800 and 2500 revolutions per minute, operating for 13-17 minutes, performing high-speed centrifugation, and filtering out the finally prepared high-purity gold powder.
2. The method for preparing high-purity gold nanoparticles with controllable size according to claim 1, wherein the fine control of growth conditions in step (3) is: in the growth process, a control method of short time, low concentration, multiple frequency and staging is adopted, the shaking time of each time is controlled to be not more than 1 minute, the standing time is not more than 10 minutes, the chloroauric acid solution and the reducing agent solution are controlled to be not more than 0.02mol/L, and the gold nanoparticles are grown in stages by taking care of adding multiple times with low concentration when the solution is added; in this preparation, the reducing agent is selected as: ascorbic acid, sodium bromide and sodium citrate.
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Non-Patent Citations (1)
| Title |
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| 飞秒激光烧蚀氯金酸水溶液制备金纳米粒子;杜传梅等;《中国激光》;20170810;第44卷(第8期);第1-9页 * |
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