A method for preparing nano silver by a multi-liquid phase method

Abstract

The present invention relates to the technical field of the preparation of nano-silver materials, and particularly to a method for preparing nano-silver by a multi-liquid phase method. A method for preparing nano-silver by a multi-liquid phase method includes the following steps: Step S1, preparing liquid A: uniformly mixing a mixed surfactant, an organic silver source and an oil-soluble organic solvent to obtain liquid A, wherein the mixed surfactant is a mixture of two or more organic amines, and the mixed surfactant includes at least one saturated amine and at least one unsaturated amine; Step S2, preparing liquid B: dissolving a reducing agent in water to obtain liquid B. The method for preparing nano-silver by the multi-liquid phase method can prepare nano-silver particles with good dispersion and uniform size, achieve the effect of controlling the dispersion of silver powder, and has simple operation and low requirements for equipment, being suitable for large-scale industrial production, and solving the problems of poor dispersion and uneven particle size of the nano-silver particles prepared by the existing nano-silver preparation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing nano silver materials, and particularly relates to a method for preparing nano silver by a multi-liquid phase method. Background Art

[0002] The noble metal material silver has excellent electrical conductivity, which is the highest among metals, and the cost is the lowest among noble metals. Silver has good oxidation resistance and solderability, and has good adhesion and other advantages. Nanotechnology is a key area of modern research and has great scientific significance. When the size reaches a certain range, their physical and chemical properties will change. Due to the nano-size effect, the surface activity, catalytic performance and antibacterial ability of nano silver are greatly improved, and it has broad application prospects in many fields: such as being used as a catalyst, antibacterial material, medical material and electronic paste, etc., and is a major research hotspot in the future.

[0003] There are various methods for preparing nano silver: currently, common methods include liquid phase reduction method, photoinduced method, seed method, mechanical ball milling method, evaporation condensation method and plant reduction method, etc. Among them, the liquid phase reduction method is to add a reducing agent to a silver salt solution to reduce silver ions into nano silver particles. The advantages are simple operation and being conducive to large-scale production.

[0004] Electronic paste is the core of power device electrical energy conversion and circuit control. With the application and development of new energy, the requirements for electronic paste are getting higher and higher. Nano silver has very broad application prospects in the field of electronic paste and can achieve "low-temperature sintering and high-temperature service" by virtue of its excellent performance. However, in the application of electronic paste, it is required that nano silver particles have good dispersibility, otherwise the performance will be affected after nano silver agglomerates.

[0005] As early as in 2007, the US patent US7850933B2

NANOPARTICLES, METHODS OF MAKING, AND APPLICATIONS USING SAME

[0006] In view of the problems raised in the background art, the object of the present invention is to provide a method for preparing silver nanoparticles by a multi-liquid phase method, which can prepare silver nanoparticles with good dispersibility and uniform sizes, achieve the effect of controlling the dispersion of silver powder, and has simple operations, low equipment requirements, and is suitable for large-scale industrial production, solving the problems of poor dispersibility and uneven particle sizes of silver nanoparticles prepared by existing silver nanoparticle preparation methods.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0009] Step S1, preparing liquid A: uniformly mixing a mixed surfactant, an organic silver source, and an oil-soluble organic solvent to obtain liquid A. The mixed surfactant is a mixture of two or more organic amines, and the mixed surfactant includes at least one saturated amine and at least one unsaturated amine;

[0010] Step S2, preparing liquid B: dissolving a reducing agent in water to obtain liquid B;

[0011] Step S3: Add the B liquid prepared in Step S2 to the A liquid prepared in Step S1 for reaction. After the reaction, a reactant with oil phase and water phase separation is obtained.

[0012] Step S4: Precipitate the oil phase of the reactant with a precipitation solution to obtain silver nanoparticles.

[0013] Furthermore, in Step S1, the chemical structural formula of the saturated amine is H 2 N-R 1 , and the chemical structural formula of the unsaturated amine is H 2 N-R 2 ;

[0014] The saturated amine means that the R 1 group is a linear alkyl group with a carbon chain length of 3 to 30;

[0015] The unsaturated amine means that the R 2 group is an unsaturated aliphatic hydrocarbon group with a carbon chain length of 3 to 30, containing a carbon-carbon double bond.

[0016] Furthermore, in the mixed surfactant, the unsaturated amine accounts for 50% to 80% of the total mass of the mixed surfactant, and the saturated amine accounts for 20% to 50% of the total mass of the mixed surfactant;

[0017] The molar concentration of the unsaturated amine in the A liquid is 0.1 mol / L to 0.35 mol / L, and the molar concentration of the saturated amine in the A liquid is 0.1 mol / L to 0.45 mol / L.

[0018] Furthermore, the saturated amine is any one selected from dodecylamine, hexadecylamine, and octadecylamine, and the unsaturated amine is selected from oleylamine.

[0019] Furthermore, the mixed surfactant is a mixture of dodecylamine and oleylamine.

[0020] Furthermore, in Step S3, add the B liquid prepared in Step S2 to the A liquid prepared in Step S1 for reaction, where the volume ratio of the A liquid to the B liquid is 1:1.

[0021] Furthermore, in Step S1, the organic silver source is any one selected from silver acetate, silver oleate, and silver stearate;

[0022] The oil-soluble organic solvent is any one selected from toluene and cyclohexane;

[0023] The molar concentration of the organic silver source in the A liquid is 0.05 mol / L to 0.1 mol / L.

[0024] Further explanation: In step S2, the reducing agent is a water-soluble reducing agent, and the reducing agent is selected from any one of sodium borohydride and potassium borohydride;

[0025] The molar concentration of the reducing agent in solution B is 0.1 mol / L to 0.15 mol / L.

[0026] Further explanation: In step S3, the reaction temperature for adding solution B prepared in step S2 to solution A prepared in step S1 is 30°C to 60°C, and the reaction time is 60 to 90 minutes.

[0027] Further explanation: The particle size of the silver nanoparticles is 2 nm to 15 nm.

[0028] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0029] By mixing saturated amine and unsaturated amine as surfactants, silver nanoparticles with good dispersibility and uniform size can be prepared, achieving the effect of controlling the dispersion of silver powder. Moreover, the operation is simple, the requirements for equipment are low, and it is suitable for large-scale industrial production, solving the problems of poor dispersibility and uneven particle size of silver nanoparticles prepared by existing preparation methods. The particle size of the silver nanoparticles synthesized by this multi-liquid-phase method for preparing silver nanoparticles is 2 nm to 15 nm, with good dispersibility and a consistent spherical shape. Description of the Drawings

[0030] Figure 1 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Example 1 of the present invention;

[0031] Figure 2 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Example 2 of the present invention;

[0032] Figure 3 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Example 3 of the present invention;

[0033] Figure 4 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Example 4 of the present invention;

[0034] Figure 5 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Comparative Example 1 of the present invention;

[0035] Figure 6 is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Comparative Example 2 of the present invention;

[0036] Figure 7It is the transmission electron microscope image (TEM image) of the silver nanoparticles obtained in Comparative Example 3 of the present invention;

[0037] Figure 8 It is the thermogravimetric curve TG graph of the silver nanoparticles obtained in Example 1 of the present invention (heating rate: 10 °C / min);

[0038] Figure 9 It is the thermogravimetric curve TG graph of the silver nanoparticles obtained in Comparative Example 2 of the present invention (heating rate: 10 °C / min).

[0039] Figure 10 It is the thermogravimetric curve TG graph of the silver nanoparticles obtained in Comparative Example 3 of the present invention (heating rate: 10 °C / min). Detailed implementation manners

[0040] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0041] Step S1, preparing liquid A: uniformly mixing a mixed surfactant, an organic silver source and an oil-soluble organic solvent to obtain liquid A, wherein the mixed surfactant is a mixture of two or more organic amines, and the mixed surfactant includes at least one saturated amine and at least one unsaturated amine;

[0042] Step S2, preparing liquid B: dissolving a reducing agent in water to obtain liquid B;

[0043] Step S3, adding the liquid B prepared in Step S2 to the liquid A prepared in Step S1 for reaction, and after the reaction is completed, a reactant with separated oil phase and water phase is obtained;

[0044] Step S4, precipitating the oil phase of the reactant with a precipitation liquid to obtain silver nanoparticles.

[0045] In the present invention, by adopting a multi-liquid-phase reduction method, silver ions and a reducing agent are respectively dissolved in immiscible solvents. The aqueous phase containing the reducing agent and the oil phase containing a mixed surfactant and an organic silver source are immiscible. The silver salt is mixed with the mixed surfactant and then complexed into an oil-soluble organic solvent. The reducing agent is dissolved in the aqueous phase. Since the surfactant is a mixture of two or more organic amines, the mixed surfactant includes at least one saturated amine and at least one unsaturated amine. The silver amine complex and the reducing agent are respectively in the oil phase and the aqueous phase, and these two phases are immiscible. When the silver amine complex moves to the oil-water two-phase interface, it reacts with the reducing agent to be reduced to silver. At the same time, the mixed surfactant wraps the surface of the produced silver to form a protective agent (the protective agent is a mixture of saturated amine and unsaturated amine), and generates steric hindrance, isolating between crystal nuclei and between crystal nuclei and crystal grains, and preventing the crystal grains from further growing. Since the unsaturated amine contains carbon-carbon double bonds, the steric hindrance generated by the hydrocarbon group containing carbon-carbon double bonds becomes larger. Therefore, after adding the unsaturated amine, the steric hindrance of the mixed surfactant is greater, and the ability to control the particle size and stability of silver particles is stronger, which can limit the processes of nucleation, growth, and aggregation of nanoparticles, thereby preparing nanosilver particles with better dispersion and more uniform size.

[0046] In the present invention, by mixing saturated amine and unsaturated amine as surfactants, nanosilver particles with good dispersion and uniform size can be prepared, achieving the effect of controlling the dispersion of silver powder. Moreover, the operation is simple, the requirements for equipment are low, and it is suitable for large-scale industrial production, solving the problems of poor dispersion and uneven particle size of nanosilver particles prepared by existing nanosilver preparation methods. The particle size of the nanosilver particles synthesized by the multi-liquid-phase method for preparing nanosilver in the present invention is 2 nm to 15 nm, with good dispersion and a consistent spherical shape.

[0047] Furthermore, in the step S1, the chemical structural formula of the saturated amine is H 2 N-R 1 , and the chemical structural formula of the unsaturated amine is H 2 N-R 2 ;

[0048] The saturated amine means that the R 1 group is a linear alkane group with a carbon chain length of 3 to 30;

[0049] The unsaturated amine means that the R 2 group is an unsaturated aliphatic hydrocarbon group with a carbon chain length of 3 to 30 and contains carbon-carbon double bonds.

[0050] In order to solve the problem of poor dispersibility of the prepared silver nanoparticles, a mixture of two or more organic amines is used as a surfactant, wherein the mixed surfactant contains at least one saturated amine and at least one unsaturated amine, and the chemical structural formulas of the saturated amine and the unsaturated amine are respectively H 2 N-R 1 and H 2 N-R 2 , where the saturated amine means that the R 1 group is a linear alkyl group with a carbon chain length of 3 to 30, containing only carbon-carbon single bonds, and H is a hydrogen atom; the unsaturated amine means that the R 2 group is an unsaturated aliphatic hydrocarbon group with a carbon chain length of 3 to 30, containing a carbon-carbon double bond, and H is a hydrogen atom. Since the unsaturated amine contains a carbon-carbon double bond, the steric hindrance generated by the hydrocarbon group containing the carbon-carbon double bond becomes larger. Therefore, after adding the unsaturated amine, the steric hindrance of the mixed surfactant is greater, and the control ability of the particle size and stability of the silver particles is stronger, which can limit the processes of nucleation, growth, aggregation, etc. of the nanoparticles, thereby preparing silver nanoparticles with better dispersibility and more uniform size.

[0051] Preferably, in the mixed surfactant, the unsaturated amine accounts for 50% to 80% of the total mass of the mixed surfactant, and the saturated amine accounts for 20% to 50% of the total mass of the mixed surfactant;

[0052] The molar concentration of the unsaturated amine in solution A is 0.1 mol / L to 0.35 mol / L, and the molar concentration of the saturated amine in solution A is 0.1 mol / L to 0.45 mol / L.

[0053] Specifically, the mixed surfactant is a mixture of saturated amine and unsaturated amine with different mass ratios, and the mass ratio when the unsaturated amine and the saturated amine are mixed is within a certain range, which controls the dispersion effect and particle size uniformity of the prepared silver nanoparticles.

[0054] Preferably, in the mixed surfactant, the unsaturated amine accounts for 60% to 70% of the total mass of the mixed surfactant, and the saturated amine accounts for 30% to 40% of the total mass of the mixed surfactant; more preferably, in the mixed surfactant, the unsaturated amine accounts for 70% of the total mass of the mixed surfactant, and the saturated amine accounts for 30% of the total mass of the mixed surfactant. At this time, the dispersion effect of the prepared silver nanoparticles is the best, and the size uniformity effect is the best.

[0055] Preferably, the saturated amine is any one selected from dodecylamine, hexadecylamine, and octadecylamine, and the unsaturated amine is selected from oleylamine.

[0056] In the present invention, the mixed surfactant adopts a combination of saturated amine and unsaturated amine. Since the unsaturated amine contains a carbon-carbon double bond, the steric hindrance generated by the hydrocarbon group containing the carbon-carbon double bond becomes larger. Therefore, after adding the unsaturated amine, the mixed surfactant has a greater steric hindrance and stronger control ability over the particle size and stability of silver particles, which can limit the processes of nucleation, growth, aggregation, etc. of nanoparticles, thereby preparing nanosilver particles with better dispersion and more uniform size.

[0057] Preferably, the mixed surfactant is a mixture of dodecylamine and oleylamine.

[0058] When the mixed surfactant is a mixture of dodecylamine and oleylamine, the prepared nanosilver particles have the best dispersion effect and the best size uniformity effect.

[0059] Preferably, in step S3, the liquid B prepared in step S2 is added to the liquid A prepared in step S1 for reaction, and the volume ratio of liquid A to liquid B is 1:1.

[0060] By slowly adding the liquid B prepared in step S2 to the liquid A prepared in step S1 for reaction, when the silver amine complex moves to the oil-water two-phase interface, it reacts with the reducing agent to be reduced to silver. At the same time, the mixed surfactant wraps the surface of the generated silver to form a protective agent and generates steric hindrance, isolating between crystal nuclei and between crystal nuclei and grains, and preventing the grains from further growing.

[0061] Furthermore, in step S1, the organic silver source is selected from any one of silver acetate, silver oleate, and silver stearate;

[0062] The oil-soluble organic solvent is selected from any one of toluene and cyclohexane;

[0063] The molar concentration of the organic silver source in liquid A is 0.05 mol / L to 0.1 mol / L.

[0064] By mixing the mixed surfactant, organic silver source, and oil-soluble organic solvent evenly, the oil phase containing the mixed surfactant and organic silver source in liquid A is immiscible with the water phase containing the reducing agent in liquid B. When the silver amine complex moves to the oil-water two-phase interface, it reacts with the reducing agent to be reduced to silver, realizing the preparation of nanosilver particles by the multi-liquid phase method. Among them, the molar concentration of the organic silver source is relatively high, which is suitable for large-scale production applications.

[0065] Furthermore, in step S2, the reducing agent is a water-soluble reducing agent, and the reducing agent is selected from any one of sodium borohydride and potassium borohydride;

[0066] The molar concentration of the reducing agent in liquid B is 0.1 mol / L to 0.15 mol / L.

[0067] By dissolving a reducing agent in water, the water containing the reducing agent in the resulting liquid B is immiscible with the oil phase containing the mixed surfactant and the organic silver source in the liquid A. When the silver amine complex moves to the oil-water two-phase interface, it reacts with the reducing agent to be reduced to silver, realizing the preparation of silver nanoparticles by the multi-liquid phase method.

[0068] Preferably, in the step S3, when adding the liquid B prepared in the step S2 to the liquid A prepared in the step S1 for reaction, the reaction temperature is 30°C to 60°C, and the reaction time is 60 to 90 min.

[0069] If the reaction temperature in the step S3 is too high, the silver nanoparticles will agglomerate severely. If the reaction temperature in the step S3 is too low, it will lead to insufficient reaction energy, and the reaction will be very slow or even not occur.

[0070] Preferably, the precipitation liquid is a methanol / acetone mixed solution, in which methanol and acetone are mixed according to a volume ratio of 1:1, and the volume ratio of the precipitation liquid to the liquid A is 1:1. After the reaction in the step S3 ends, a phenomenon of oil phase and water phase stratification will occur. The oil phase is precipitated, washed with the precipitation liquid and then filtered to obtain silver nanoparticles.

[0071] Preferably, the particle size of the silver nanoparticles is 2 nm to 15 nm.

[0072] The synthesis method of the present invention is conducive to the large-scale industrial preparation of silver nanoparticles with a particle size below 20 nm. The particle size of the synthesized silver nanoparticles is 2 nm to 15 nm, with good dispersion and a consistent spherical shape.

[0073] For the convenience of understanding the present invention, the present invention will be described more comprehensively below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0074] For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0075] Example 1

[0076] A method for preparing silver nanoparticles by the multi-liquid phase method, comprising the following steps:

[0077] Step S1: Prepare Solution A: Mix the mixed surfactant, organic silver source and oil-soluble organic solvent evenly to obtain Solution A. The mixed surfactant is a mixture of dodecylamine and oleylamine, where dodecylamine is a saturated amine and oleylamine is an unsaturated amine. The proportion of the saturated amine in the total mass of the mixed surfactant and the proportion of the unsaturated amine in the total mass of the mixed surfactant are shown in Table 1 below. The organic silver source is silver acetate, and the oil-soluble organic solvent is toluene. The molar concentration of the unsaturated amine in Solution A is 0.2 mol / L, the molar concentration of the saturated amine in Solution A is 0.13 mol / L, and the molar concentration of the organic silver source in Solution A is 0.07 mol / L;

[0078] Step S2: Prepare Solution B: Dissolve the reducing agent in water. The reducing agent is sodium borohydride, and the molar concentration of the reducing agent in Solution B is 0.13 mol / L to obtain Solution B;

[0079] Step S3: Add Solution B prepared in Step S2 to Solution A prepared in Step S1 for reaction, where the volume ratio of Solution A to Solution B is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with oil-phase and water-phase separation is obtained;

[0080] Step S4: Wash the oil phase of the reactant with the precipitation solution and then filter. The precipitation solution is a methanol / acetone mixed solution, and the volume ratio of the precipitation solution to Solution A is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as shown in Figure 1 shown, and the TG image of the obtained silver nanoparticles is as shown in Figure 8 shown.

[0081] Example 2

[0082] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0083] Step S1: Prepare Solution A: Mix the mixed surfactant, organic silver source and oil-soluble organic solvent evenly to obtain Solution A. The mixed surfactant is a mixture of dodecylamine and oleylamine, where dodecylamine is a saturated amine and oleylamine is an unsaturated amine. The proportion of the saturated amine in the total mass of the mixed surfactant and the proportion of the unsaturated amine in the total mass of the mixed surfactant are shown in Table 1 below. The organic silver source is silver acetate, and the oil-soluble organic solvent is toluene. The molar concentration of the unsaturated amine in Solution A is 0.18 mol / L, the molar concentration of the saturated amine in Solution A is 0.17 mol / L, and the molar concentration of the organic silver source in Solution A is 0.07 mol / L;

[0084] Step S2: Prepare Solution B: Dissolve the reducing agent in water. The reducing agent is sodium borohydride, and the molar concentration of the reducing agent in Solution B is 0.13 mol / L to obtain Solution B;

[0085] Step S3: Add the B liquid prepared in Step S2 to the A liquid prepared in Step S1 for reaction. The volume ratio of the A liquid to the B liquid is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with a separated oil phase and water phase is obtained;

[0086] Step S4: Wash the oil phase of the reactant with a precipitation liquid and then filter it. The precipitation liquid is a methanol / acetone mixed solution, and the volume ratio of the precipitation liquid to the A liquid is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as Figure 2 shown.

[0087] Example 3

[0088] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0089] Step S1: Prepare the A liquid: Mix the mixed surfactant, organic silver source, and oil-soluble organic solvent evenly to obtain the A liquid. The mixed surfactant is a mixture of dodecylamine and oleylamine. Among them, dodecylamine is a saturated amine, and oleylamine is an unsaturated amine. The proportion of the saturated amine in the total mass of the mixed surfactant and the proportion of the unsaturated amine in the total mass of the mixed surfactant are shown in Table 1 below. The organic silver source is silver acetate, and the oil-soluble organic solvent is toluene. The molar concentration of the unsaturated amine in the A liquid is 0.15 mol / L, the molar concentration of the saturated amine in the A liquid is 0.22 mol / L, and the molar concentration of the organic silver source in the A liquid is 0.07 mol / L;

[0090] Step S2: Prepare the B liquid: Dissolve the reducing agent in water. The reducing agent is sodium borohydride, and the molar concentration of the reducing agent in the B liquid is 0.13 mol / L to obtain the B liquid;

[0091] Step S3: Add the B liquid prepared in Step S2 to the A liquid prepared in Step S1 for reaction. The volume ratio of the A liquid to the B liquid is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with a separated oil phase and water phase is obtained;

[0092] Step S4: Wash the oil phase of the reactant with a precipitation liquid and then filter it. The precipitation liquid is a methanol / acetone mixed solution, and the volume ratio of the precipitation liquid to the A liquid is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as Figure 3 shown.

[0093] Example 4

[0094] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0095] Step S1: Prepare Solution A: Mix the mixed surfactant, organic silver source and oil-soluble organic solvent evenly to obtain Solution A. The mixed surfactant is a mixture of dodecylamine and oleylamine, where dodecylamine is a saturated amine and oleylamine is an unsaturated amine. The mass percentages of the saturated amine and the unsaturated amine in the total mass of the mixed surfactant are shown in Table 1 below. The organic silver source is silver acetate, the oil-soluble organic solvent is toluene. The molar concentration of the unsaturated amine in Solution A is 0.24 mol / L, the molar concentration of the saturated amine in Solution A is 0.1 mol / L, and the molar concentration of the organic silver source in Solution A is 0.07 mol / L;

[0096] Step S2: Prepare Solution B: Dissolve the reducing agent in water. The reducing agent is sodium borohydride. The molar concentration of the reducing agent in Solution B is 0.13 mol / L to obtain Solution B;

[0097] Step S3: Add Solution B prepared in Step S2 to Solution A prepared in Step S1 for reaction. The volume ratio of Solution A to Solution B is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with separated oil phase and water phase is obtained;

[0098] Step S4: Wash the oil phase of the reactant with the precipitation solution and then filter. The precipitation solution is a methanol / acetone mixed solution. The volume ratio of the precipitation solution to Solution A is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as Figure 4 shown.

[0099] Comparative Example 1

[0100] A method for preparing silver nanoparticles by a multi-liquid phase method, comprising the following steps:

[0101] Step S1: Prepare Solution A: Mix the mixed surfactant, organic silver source and oil-soluble organic solvent evenly to obtain Solution A. The mixed surfactant is a mixture of dodecylamine and oleylamine, where dodecylamine is a saturated amine and oleylamine is an unsaturated amine. The mass percentages of the saturated amine and the unsaturated amine in the total mass of the mixed surfactant are shown in Table 1 below. The organic silver source is silver acetate, the oil-soluble organic solvent is toluene. The molar concentration of the unsaturated amine in Solution A is 0.12 mol / L, the molar concentration of the saturated amine in Solution A is 0.26 mol / L, and the molar concentration of the organic silver source in Solution A is 0.07 mol / L;

[0102] Step S2: Prepare Solution B: Dissolve the reducing agent in water. The reducing agent is sodium borohydride. The molar concentration of the reducing agent in Solution B is 0.13 mol / L to obtain Solution B;

[0103] Step S3: Add the B liquid prepared in Step S2 into the A liquid prepared in Step S1 for reaction. The volume ratio of the A liquid to the B liquid is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with oil-phase and water-phase separation is obtained;

[0104] Step S4: Wash the oil phase of the reactant with a precipitation liquid and then filter it. The precipitation liquid is a methanol / acetone mixed solution, and the volume ratio of the precipitation liquid to the A liquid is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as Figure 5 shown.

[0105] Comparative Example 2

[0106] A method for preparing silver nanoparticles, comprising the following steps:

[0107] Step S1: Prepare the A liquid: Mix a surfactant, an organic silver source, and an oil-soluble organic solvent evenly to obtain the A liquid. The surfactant is dodecylamine, where dodecylamine is a saturated amine, the organic silver source is silver acetate, and the oil-soluble organic solvent is toluene. The molar concentration of the surfactant in the A liquid is 0.45 mol / L, and the molar concentration of the organic silver source in the A liquid is 0.07 mol / L;

[0108] Step S2: Prepare the B liquid: Dissolve a reducing agent in water. The reducing agent is sodium borohydride, and the molar concentration of the reducing agent in the B liquid is 0.13 mol / L to obtain the B liquid;

[0109] Step S3: Add the B liquid prepared in Step S2 into the A liquid prepared in Step S1 for reaction. The volume ratio of the A liquid to the B liquid is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with oil-phase and water-phase separation is obtained;

[0110] Step S4: Wash the oil phase of the reactant with a precipitation liquid and then filter it. The precipitation liquid is a methanol / acetone mixed solution, and the volume ratio of the precipitation liquid to the A liquid is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as Figure 6 shown, and the TG curve is as Figure 9 shown.

[0111] Comparative Example 3

[0112] A method for preparing silver nanoparticles, comprising the following steps:

[0113] Step S1: Prepare the A liquid: Mix a surfactant, an organic silver source, and an oil-soluble organic solvent evenly to obtain the A liquid. The surfactant is oleylamine, where oleylamine is an unsaturated amine, the organic silver source is silver acetate, and the oil-soluble organic solvent is toluene. The molar concentration of the surfactant in the A liquid is 0.31 mol / L, and the molar concentration of the organic silver source in the A liquid is 0.07 mol / L;

[0114] Step S2: Prepare Solution B: Dissolve the reducing agent in water. The reducing agent is sodium borohydride, and the molar concentration of the reducing agent in Solution B is 0.13 mol / L to obtain Solution B.

[0115] Step S3: Add Solution B prepared in Step S2 to Solution A prepared in Step S1 for reaction. The volume ratio of Solution A to Solution B is 1:1, the reaction temperature is 40 °C, and the reaction time is 70 min. After the reaction, a reactant with oil-phase and water-phase separation is obtained.

[0116] Step S4: Wash the oil phase of the reactant with a precipitation solution and then filter it. The precipitation solution is a methanol / acetone mixed solution, and the volume ratio of the precipitation solution to Solution A is 1:1 to obtain silver nanoparticles. The TEM image of the obtained silver nanoparticles is as shown in Figure 7 shown, and the TG curve is as shown in Figure 10 shown.

[0117] Table 1 Proportion of surfactant addition, dispersion and size distribution of products in Examples 1-4 and Comparative Examples 1-3

[0118]

[0119] As can be seen from the above table and the comparison with Figures 1 to 7 , the silver nanoparticles prepared in Example 1 have good dispersion effect and uniform size. It can also be seen from the TG curve of the silver powder in Figure 8 Example 1 that after the temperature reaches 300 °C, the weight of the silver powder hardly decreases any more, indicating that the protective agent on the surface of the silver powder volatilizes. From the perspective of weight change, the protective agent on the surface of the silver powder only accounts for 5-6% wt of the weight of the silver powder. The purity of the powder ensures the product quality, which is of great significance for the promotion and industrialization of the product. As shown in the TG curves of the silver powder in Figure 9 (Comparative Example 2) and Figure 10 (Comparative Example 3), from the perspective of weight change, the protective agent on the surface of the silver powder accounts for about 20% wt of the weight of the silver powder. The more protective agent on the surface of the silver powder, the more it will affect the performance of the silver powder. Therefore, after adding unsaturated amine (oleylamine), the performance of the silver powder has been improved in terms of size, dispersion and content of the protective agent on the surface, etc.

[0120] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing nano-silver by a multi-liquid phase method, characterized in that, it comprises the following steps: Step S1: Prepare liquid A: Mix a mixed surfactant, an organic silver source and an oil-soluble organic solvent evenly to obtain liquid A. The mixed surfactant is a mixture of two or more organic amines, and the mixed surfactant includes at least one saturated amine and at least one unsaturated amine; Step S2: Prepare liquid B: Dissolve a reducing agent in water to obtain liquid B; the oil phase containing the mixed surfactant and the organic silver source in liquid A is immiscible with the water phase containing the reducing agent in liquid B; Step S3: Add the liquid B prepared in Step S2 to the liquid A prepared in Step S1. The reaction temperature is 30°C to 60°C, and the reaction time is 60 to 90 minutes. After the reaction, a reactant with separated oil phase and water phase is obtained; Step S4: Precipitate the oil phase of the reactant with a precipitation solution to obtain nano-silver particles, and the particle size of the nano-silver particles is 2 nm to 15 nm; In the step S1, the chemical structural formula of the saturated amine is H 2 N-R 1 , and the chemical structural formula of the unsaturated amine is H 2 N-R 2 ; A saturated amine means that R 1 group is a linear alkyl group with a carbon chain length of 3 to 30; An unsaturated amine means that R 2 group is an unsaturated aliphatic hydrocarbon group with a carbon chain length of 3 to 30 and contains a carbon-carbon double bond; In the mixed surfactant, the unsaturated amine accounts for 50% to 80% of the total mass of the mixed surfactant, and the saturated amine accounts for 20% to 50% of the total mass of the mixed surfactant; The molar concentration of the unsaturated amine in liquid A is 0.1 mol / L to 0.35 mol / L, and the molar concentration of the saturated amine in liquid A is 0.1 mol / L to 0.45 mol / L.

2. The method for preparing nano-silver by a multi-liquid phase method according to claim 1, characterized in that, the saturated amine is any one selected from dodecylamine, hexadecylamine and octadecylamine, and the unsaturated amine is selected from oleylamine.

3. The method for preparing nano-silver by a multi-liquid phase method according to claim 2, characterized in that, the mixed surfactant is a mixture of dodecylamine and oleylamine.

4. The method for preparing nano-silver by a multi-liquid phase method according to claim 1, characterized in that, in Step S3, when reacting by adding the liquid B prepared in Step S2 to the liquid A prepared in Step S1, the volume ratio of liquid A to liquid B is 1:

1.

5. The method for preparing nano-silver by a multi-liquid phase method according to claim 1, characterized in that, in Step S1, the organic silver source is any one selected from silver acetate, silver oleate and silver stearate; the oil-soluble organic solvent is any one selected from toluene and cyclohexane; the molar concentration of the organic silver source in liquid A is 0.05 mol / L to 0.1 mol / L.

6. The method for preparing nano-silver by a multi-liquid phase method according to claim 1, characterized in that, in Step S2, the reducing agent is a water-soluble reducing agent, and the reducing agent is any one selected from sodium borohydride and potassium borohydride; the molar concentration of the reducing agent in liquid B is 0.1 mol / L to 0.15 mol / L.

Images