Method for continuously preparing octahedral copper powder based on dynamic tube solvothermal synthesis method

Abstract

The invention discloses a method for continuously preparing octahedral copper powder based on a dynamic tube solvothermal synthesis method. A copper source, a surfactant and a solvent are mixed and then placed on a magnetic stirrer to be fully dissolved and stirred; dissolving sodium hydroxide in a solvent, adding into the system, uniformly stirring and dispersing, injecting into a dynamic tubular reactor through a plunger pump, and synthesizing octahedral copper powder through solvothermal reaction. According to the method, the dynamic tube reactor is combined with the plunger pump, so that continuous preparation of the material is realized, and enlarged production and preparation under a solvothermal condition become possible. Due to the small reaction cavity and the strong convection effect, the mass transfer and heat transfer of the material can be effectively improved, and the environment consistency in the material synthesis process is improved, so that the uniformity of the material is improved. According to the preparation method, a solvothermal method is utilized for preparation, use of a strong reducing agent is avoided, the preparation cost is further reduced, and preparation of the octahedral nano copper powder is achieved.

Description

Technical Field

[0001] The invention belongs to the field of precious metal materials, and in particular relates to a method for continuously preparing octahedral copper powder based on a dynamic tube solvent thermal synthesis method. Background Art

[0002] Copper powder is a common metal material widely used in people's daily life and actual production. Compared with precious metals such as Au, Ag, Pd and Pt, Cu is abundant and cheap. It has excellent conductivity among metals, second only to Ag. It is often used as conductive materials, electrode materials, solid lubricants, high-efficiency catalysts, engineering materials, etc., and is widely used in electronic information, energy and electricity, petrochemicals, light industry and textiles, industrial engineering and other fields.

[0003] Copper octahedron, as a copper structure with a specific geometric shape, has a larger specific surface area than other shapes (such as cubes), which means that it can provide more active sites for catalytic reactions. The Cu(111) crystal plane is a unique crystal plane in the copper octahedron structure, and it has shown significant advantages in many applications. These advantages are mainly reflected in catalytic activity, antioxidant ability, surface oxygen species characteristics, and electrical and thermal conductivity. "German Applied Chemistry" (Angew.Chem. Int. Ed. 2024, Vol. 63, No. 11) pointed out that the Cu(111) crystal plane performs well in the electrocatalytic NO reduction reaction to synthesize ammonia. Compared with the Cu(100) crystal plane, the Cu(111) crystal plane achieved a higher yield (371.89 μmol cm -2 h -1 ) and Faraday efficiency (93.19%), indicating that the Cu(111) crystal plane is the dominant crystal plane for electrocatalytic NO reduction to synthesize ammonia. Nature (Nature 2022, Vol. 603, p. 434) pointed out that the Cu(111) crystal plane has excellent antioxidant capacity, which is due to its flat surface structure that can effectively prevent the diffusion of oxygen atoms and the oxidation reaction. In addition, first-principles calculations also show the beneficial effect of step edge sites on the antioxidant capacity of Cu.

[0004] The stability and dispersibility of copper powder in the medium affect its performance. Surfactants have multiple functions in the preparation of copper powder, such as improving dispersibility, controlling particle size, improving stability, affecting morphology and improving performance. By selecting the appropriate surfactant and its dosage, copper powder products with excellent performance can be prepared. European Chemistry (Chem. - Eur. J. 2012, Vol. 18, No. 44) reported that during the synthesis of Ni and Pd nanoparticles, metal (II) acetylacetonate complexes (M(acac)2 or M(C5H7O2)2) and oleylamine had rich reactivity, in which oleylamine acted as a reducing agent through oxidative dehydrogenation. Regarding the synthesis of Cu nanoparticles by reducing Cu(acac)2 with oleylamine, it was found that oleylamine was not a ligand of the nanoparticles. Instead, the ligand was a substance formed during the reaction: N-oleyl acetamide. And oleylamine is also difficult to remove in the subsequent washing process. Colloid Polym Sci. (2024, Vol. 302, p. 362) reported the RSH and particle size of copper powder after four surfactants were dispersed in SDS, SDBS, CTAB and PVP. The results showed that PVP is the most effective surfactant for dispersing Cu in aqueous media. Materials Development and Application (Vol. 22, No. 1) pointed out that when preparing ultrafine copper powder, adding an appropriate amount of PVP can make the ultrafine copper powder particles more spherical and uniform, and can effectively eliminate the agglomeration of copper powder.

[0005] Copper powder preparation is divided into gas phase method, liquid phase method and solid phase method according to the aggregation state of reactants. Both gas phase method and solid phase method have corresponding disadvantages that are difficult to overcome in preparing powder. Hunan Nonferrous Metals (Volume 3, 2015, page 62) pointed out that gas phase evaporation is the most direct and effective method for preparing metal powder. Lairliqusd Company of France used induction heating method and improved gas phase evaporation powder making technology to prepare copper ultrafine powder with a yield of 0.5 kg / h. Copper powder prepared by gas phase method is usually regular spherical, with high requirements for equipment and large investment. Copper powder prepared by solid phase method has wide particle size distribution and is easy to introduce impurities; because of the above disadvantages, the application and promotion of these preparation methods are limited. The preparation of nano copper powder by liquid phase method has its unique advantages, such as easy control of components, simple equipment, low production cost, and easy industrial production. Among them, the traditional solvent thermal synthesis method is widely used. It is a wet chemical method completed in a closed container. It uses water, ethanol and other solutions as reaction media. By heating the reaction container, a high temperature and high pressure reaction environment is formed, so that the usually insoluble or insoluble substances are dissolved and recrystallized. However, its output is very small, which is limited in large-scale industrial production. The main disadvantage of the current reactor is that the output of a single preparation is small due to the closed system; at the same time, due to the existence of a high temperature and high pressure environment, if the volume is simply expanded during the amplification process, it will be more dangerous at a low efficiency. In addition, copper powder and cuprous oxide are both present in the reactor. The presence of copper powder will accelerate the decomposition of the reducing agent, that is, increase the amount of reducing agent, and also lead to relatively poor uniformity of the particle size of the copper powder. Therefore, the uniform synthesis of copper powder can be achieved through process improvement, which can not only effectively control the particle size, but also reduce the amount of reducing agent used, so as to improve the quality of copper powder and reduce the cost. Patent CN118218603A provides a method for preparing ultrafine copper powder using a traditional solvent thermal method. The process is simple, has excellent dispersibility, antioxidant properties and controllable morphology, but cannot achieve continuous preparation, which hinders its large-scale industrial production. At the same time, the morphology and uniformity of the powder material are poor. Among the various morphologies it contains, there is no octahedral copper powder. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for continuously preparing octahedral copper powder based on a dynamic tube solvent thermal synthesis method.

[0007] The present invention realizes continuous preparation of materials by combining a dynamic tube reactor with a plunger pump, making it possible to enlarge the production and preparation under solvent thermal conditions. Due to the small reaction cavity and the strong convection effect, the mass transfer and heat transfer of the material can be effectively improved, and the consistency of the environment during the synthesis of the material can be improved, thereby improving the uniformity of the material itself; at the same time, although the cavity of the dynamic tube itself is relatively small, due to the use of a continuous production process, its production efficiency and speed can be effectively improved, significantly reducing the preparation cost of the material; the use of a solvent thermal method to prepare avoids the use of a strong reducing agent, further reduces the preparation cost, and realizes the preparation of octahedral nano copper powder.

[0008] The method for continuously preparing octahedral copper powder based on the dynamic tube solvent thermal synthesis method of the present invention comprises the following steps: The copper source, surfactant and solvent are mixed and placed on a magnetic stirrer for sufficient dissolution and stirring; then sodium hydroxide is dissolved in the solvent and added into the system, and after being stirred and dispersed evenly, it is injected into a dynamic tubular reactor through a plunger pump to synthesize octahedral copper powder through a solvent thermal reaction.

[0009] The copper source is selected from one or more of copper sulfate, copper nitrate, copper phosphate and copper acetate.

[0010] The surfactant is selected from one or more of sodium dodecyl benzoate, urea, ammonium sulfate, polyvinyl pyrrolidone, Triton X100 and benzotriazole.

[0011] The solvent is selected from one or more of methanol, ethanol, ethylene glycol, formaldehyde, acetaldehyde and isopropanol.

[0012] Furthermore, the total volume of the reaction system is controlled to be 30 mL. In the reaction system, the concentration of the copper source is 0.25 mol / L, the concentration of the surfactant is 10-20 g / L, and the concentration of the sodium hydroxide is 1.2 mol / L.

[0013] The temperature of the dynamic tubular reactor was set at 200°C, and the reaction was carried out for 15 minutes after pumping, and the dynamic tube speed was kept at 50-300 r / min. The reaction time was regulated by the pumping speed of the plunger pump. The higher the pumping speed, the shorter the residence time.

[0014] The present invention adopts a dynamic tube reactor. Due to the small reaction cavity and the strong convection effect, the mass transfer and heat transfer of the material can be effectively improved, and the uniformity of the environment during the synthesis of the material can be improved, thereby improving the uniformity of the material itself; due to the increased full contact between the solvent and the copper source during the dynamic flow process, the reduction effect of the solvent itself can be maximized, and the amount of reducing agent can be reduced to the greatest extent. At the same time, although the cavity of the dynamic tube itself is relatively small, due to the continuous production process, its production efficiency and speed can be effectively improved, significantly reducing the preparation cost of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flow chart of the preparation process of the present invention.

[0016] Figure 2 Schematic diagram of the preparation process of the present invention.

[0017] Figure 3 Under the same ratio of copper source, surfactant and reducing agent, the morphology of the material produced by the autoclave reaction (A) and the morphology of the copper powder synthesized by the dynamic tube reaction (B).

[0018] Figure 4 XRD diagram of the copper powder synthesized by the dynamic tube of the present invention.

[0019] Figure 5 Effect of surfactant on morphology (urea).

[0020] Figure 6 Effect of surfactant on morphology (sodium dodecyl sulfate).

[0021] Figure 7 Effect of surfactant concentration on morphology at low concentrations.

[0022] Figure 8 The effect of high copper salt concentration on morphology. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0024] The specific process is: 0.25 mol / L copper salt, 10 ml solvent, and 10 g / L~20 g / L surfactant were mixed and placed on a magnetic stirrer for full dissolution and stirring for 10 min. 1.2 mol / L sodium hydroxide and 20 mL solvent were added and continued to stir for 30 min. Then, the mixture was injected into a dynamic tubular reactor through a plunger pump. The temperature of the reactor was set to 200 °C. After the pumping, the mixture was reacted for 15 min. The speed of the dynamic tube was maintained at 50-300 r / min. The powder was washed and dried from the discharge port to obtain octahedral copper powder ( Figure 1and 2 ).

[0025] Scanning electron microscopy and XRD analysis show that the dynamic tube synthesis method can effectively improve the reduction effect of the solvent and obtain octahedral copper powder, making the material more uniform ( Figure 3 and Figure 4 ); At the same time, by adjusting the types of different surfactants and utilizing the coordination effect between surfactants and copper, the morphology can be made closer to an octahedron ( Figure 5 and Figure 6 ); When the surfactant content is too low, the copper powder does not form an octahedron and is unevenly dispersed ( Figure 7 ); when the surfactant content is too high, the product will foam and the material cannot be prepared stably; when the copper salt content is too high, the copper powder will not form an octahedron ( Figure 8 ), which is mainly due to the fact that the copper powder cannot be fully protected by the surfactant.

[0026] The copper source is selected from one or more of copper sulfate, copper nitrate, copper phosphate and copper acetate.

[0027] The solvent is selected from one or more of methanol, ethanol, ethylene glycol, formaldehyde, acetaldehyde and isopropanol.

[0028] The surfactant is selected from one or more of sodium dodecyl benzoate, urea, ammonium sulfate, polyvinyl pyrrolidone, Triton X100 and benzotriazole. Comparative Example 1:

[0029] Using ethanol as a solvent, a mixed solution of 0.25 mol / L copper nitrate and 14 g / L polyvinyl pyrrolidone with a total volume of 30 mL was prepared, and the mixed solution was added to the reactor, stirred at a rate of 100 rpm / min and heated to 200°C. After reaching the reaction temperature (200°C), after reacting for 5 hours, the obtained powder was washed and dried to obtain octahedral copper powder 1. Embodiment 1:

[0030] Using ethanol as the solvent, a mixed solution of 0.25 mol / L copper nitrate and 14 g / L surfactant polyvinyl pyrrolidone with a total volume of 30 mL was prepared. Subsequently, the dynamic tube was started, the stirring paddle was kept rotating at a speed of 100 r / min, and the reaction temperature in the dynamic tube was 200°C. Then, the mixed solution was pumped into the cavity of the dynamic tube at a rate of 5 mL / min using a syringe pump for reduction reaction. After reacting in the dynamic tube for 5-20 minutes, the powder discharged from the product outlet was washed and dried to obtain octahedral copper powder 2.

[0031] The octahedral copper powders in Comparative Example 1 and Example 1 were characterized by scanning electron microscopy, and Example 1 was analyzed by X-ray diffractometer. Figure 3 , 4 shown.

[0032] Figure 3 A is a scanning electron microscope (SEM) image of the octahedral copper powder 1 prepared by a reaction kettle in Comparative Example 1 of the present invention; Figure 3 B is a scanning electron microscope (SEM) image of the octahedral copper powder 2 prepared by the dynamic tube solvothermal synthesis method in Example 1 of the present invention. Figure 3 As shown in A, the surface of the octahedral copper powder 1 prepared by the reaction kettle (Comparative Example 1) is relatively rough, agglomerates, and has an uneven morphology. In contrast, the surface of the octahedral copper powder 2 prepared by the dynamic tube solvent thermal synthesis method is smooth, the morphology is very clear octahedron, and the particle size is uniform and there is no agglomeration phenomenon. Figure 3 As shown in B.

[0033] Figure 4 : is the X-ray diffraction (XRD) pattern of the octahedral copper powder 2 prepared by the dynamic tube solvent thermal synthesis method in Example 1 of the present invention. Figure 4 As shown, octahedral copper powder with a single composition can be obtained by using the dynamic tube solvothermal synthesis method. Embodiment 2:

[0034] The octahedral copper powder 3 was prepared by the same method as in Example 1, except that the surfactant used was urea. The scanning electron microscope (SEM) image of the prepared octahedral copper powder 3 is as follows: Figure 5 shown.

[0035] Figure 5 FIG. 3 is a scanning electron microscope (SEM) image of octahedral copper powder 3 prepared by the dynamic tube solvent thermal synthesis method in Example 2 of the present invention. Figure 5 As shown, the morphology of the octahedral copper powder 3 prepared by the method in Example 2 has a slightly rough surface. Embodiment 3:

[0036] Octahedral copper powder 4 was prepared by the same method as in Example 1, except that the surfactant used was sodium dodecyl sulfate. The scanning electron microscope (SEM) image of the prepared octahedral copper powder 4 is as follows: Figure 6 shown.

[0037] Figure 6 : is a scanning electron microscope (SEM) image of octahedral copper powder 4 prepared by dynamic tube solvothermal synthesis in Example 3 of the present invention. Figure 6 As shown, the octahedral copper powder 4 prepared by the method in Example 3 has an uneven morphology and a rough surface. Comparative Example 2:

[0038] Octahedral copper powder 5 was prepared by the same method as in Example 1, except that the concentration of the surfactant polyvinyl pyrrolidone was 5 g / L. The scanning electron microscope (SEM) image of the prepared octahedral copper powder 4 is shown in FIG. Figure 7 shown.

[0039] Figure 7 This is a scanning electron microscope (SEM) image of octahedral copper powder 5 prepared by dynamic tube solvent thermal synthesis in comparative example 2 of the present invention. Figure 7 As shown in the figure, when the surfactant concentration is low (less than 10 g / L), it cannot coordinate well with copper ions, resulting in a faster deposition rate of copper salts; when the surfactant concentration is high, the surfactant will be adsorbed on the surface of copper particles, affecting the further growth of the material. Comparative Example 3:

[0040] Octahedral copper powder 6 was prepared by the same method as in Example 1, except that the concentration of copper salt used was higher, 0.5 mol / L. The scanning electron microscope (SEM) image of the prepared octahedral copper powder 6 is shown in FIG. Figure 8 shown.

[0041] Figure 8 This is a scanning electron microscope (SEM) image of octahedral copper powder 6 prepared by dynamic tube solvent thermal synthesis in comparative example 3 of the present invention. Figure 8 As shown, the size of the copper powder is relatively large and very uneven. This is because the concentration of the copper salt is relatively high, and a small amount of copper ions cannot be gradually released during the growth process. The excessive concentration of copper ions leads to uneven growth of the copper powder material.

Claims

1. A method for continuously preparing octahedral copper powder based on dynamic tube solvent thermal synthesis, characterized in that The steps include: The copper source, surfactant and solvent are mixed and placed on a magnetic stirrer for sufficient dissolution and stirring; then sodium hydroxide is dissolved in the solvent and added into the system, and after being stirred and dispersed evenly, it is injected into a dynamic tubular reactor through a plunger pump to synthesize octahedral copper powder through a solvent thermal reaction.

2. The method according to claim 1, characterized in that: The copper source is selected from one or more of copper sulfate, copper nitrate, copper phosphate and copper acetate.

3. The method according to claim 1, characterized in that: The surfactant is selected from one or more of sodium dodecyl benzoate, urea, ammonium sulfate, polyvinyl pyrrolidone, Triton X100, and benzotriazole.

4. The method according to claim 1, characterized in that: The solvent is selected from one or more of methanol, ethanol, ethylene glycol, formaldehyde, acetaldehyde and isopropanol.

5. The method according to claim 1, 2, 3 or 4, characterized in that: The total volume of the reaction system was controlled to be 30 mL; in the reaction system, the concentration of the copper source was 0.25 mol / L, the concentration of the surfactant was 10-20 g / L, and the concentration of the sodium hydroxide was 1.2 mol / L.

6. The method according to claim 1, characterized in that: The temperature of the dynamic tubular reactor was set at 200°C, and the reaction was carried out for 15 min after pumping in, and the dynamic tube speed was maintained at 50-300 r / min.

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