A method for hydrothermal reduction preparation of Cu / CuO nanosheet bundles

Abstract

The application provides a method for preparing Cu / CuO nanosheet bundles by hydrothermal reduction, comprising the following steps: dissolving copper salt in water to prepare precursor solution A; dissolving a reducing agent in water to prepare solution B; the molar ratio of the reducing agent to the copper salt is 1:2-6; stirring solution B, stepwise heating to 60-120 DEG C, subcooling dropwise adding the precursor solution A, reacting for 20-40 min, adjusting the pH value of the solution to 13-14, then adding a macromolecular chain organic matter stabilizer aqueous solution, then superimposed ultrasonic reaction for 5 min-30 min at 60-120 DEG C; when the mixed solution changes from dark blue to green and then to black red, quickly cooling to room temperature to obtain a suspension; separating, washing and drying the suspension. The technical scheme of the application can quickly prepare Cu / CuO nanosheet bundles with uniform size and controllable morphology at low temperature, and the process cost is low and the efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials, and in particular relates to a method for preparing Cu / CuO nanosheet bundles by hydrothermal reduction. Background Art

[0002] Nano Cu / CuO can, by virtue of the unique surface effects, quantum size effects, volume effects, and quantum tunneling effects of nano-sized materials, exhibit unique physical and chemical properties in the fields of electricity (conductivity, superconductivity), optics (sensitive components such as sensors, photocatalytic degradation), chemical engineering (ceramics, glass, antibacterial agents), mechanics (superplasticity, high hardness and strength), and military (propellants and fuel accelerators, infrared absorption function), and has a wide range of applications. In recent years, researchers have actively explored the synthesis of nano Cu / CuO with different morphologies, including nanoparticles, nanowires, nanosheets, porous, hollow microspheres and other structures. Among them, irregularly shaped (for example, flower-shaped) nano Cu / CuO has attracted much attention due to its larger specific surface area, higher reaction activity, lower reaction temperature, and more stable physical and chemical properties.

[0003] Currently, the main methods for synthesizing nano Cu / CuO include template methods, coprecipitation methods, hydrothermal reduction methods, and sonochemical methods. The template used in the template method must be removed after the synthesis reaction through steps such as corrosion, which damages the synthesized nano Cu / CuO to a certain extent. Furthermore, the template method has a low yield. Without the protection of an inducing agent, Cu / CuO synthesized by the precipitation method exhibits poor morphological and size uniformity. The hydrothermal reduction method offers advantages such as morphological controllability and ease of operation, making it suitable for forming phases with various morphologies and special structures. It requires low reaction conditions and is easy to operate. However, this method requires high reaction temperatures and long reaction times (often requiring a high-temperature reactor). Furthermore, the morphological and size uniformity of nano Cu / CuO synthesized by the hydrothermal method currently remains insufficient, limiting its application. While the sonochemical hydrothermal reduction method leverages the localized high temperature and high pressure environment generated by the acoustic cavitation effect, it can significantly increase the reaction rate. However, the reaction is difficult to control, and microwave reactors are expensive and costly, limiting their use to small-scale production. Therefore, a new synthetic method for rapidly preparing nano Cu / CuO with controllable morphology and size is urgently needed. Summary of the Invention

[0004] In response to the above technical problems, the present invention discloses a method for preparing Cu / CuO nanosheets by hydrothermal reduction, which solves the problems of poor morphology and size uniformity, high cost and low yield in the prior art of synthesizing nano Cu / CuO.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] A method for preparing Cu / CuO nanosheets by hydrothermal reduction comprises the following steps:

[0007] Step S1, dissolving copper salt in water to prepare precursor solution A;

[0008] Step S2, dissolving a reducing agent in water to prepare a solution B; the reducing agent is one or a mixture of two or more of sodium citrate, polyethylene glycol, and glucose;

[0009] Step S3, stirring solution B, step-by-step heating to 60-120°C, adding precursor solution A dropwise, reacting for 20-40 minutes, and obtaining solution C; wherein, the molar ratio of the reducing agent to the copper salt is 1:2-6, and the temperature of the added precursor solution A is lower than 15°C; the step-by-step heating refers to first rapidly heating to 50°C at a heating rate of not less than 12°C / min, and then slowly heating to the reaction temperature of 60-120°C at a heating rate of not more than 8°C / min; here, maintaining rapid heating and slow heating to reach the reaction temperature to promote "explosive" nucleation.

[0010] Step S4, adding alkali to solution C to adjust the pH of the solution to 13-14, then adding an aqueous solution of a macromolecular chain organic stabilizer to obtain a dark blue mixed solution, superimposing an ultrasonic reaction on the mixed solution at 60-120° C. for 5-30 minutes; when the mixed solution changes from dark blue to green and then to black-red, placing it in a cooling medium or a cooling environment and rapidly cooling it to room temperature to obtain a suspension; wherein the macromolecular chain organic stabilizer is one or a mixture of two or more of polyvinyl pyrrolidone, bovine serum albumin, and polydimethyldiallyl ammonium chloride;

[0011] Step S5, separating, washing, and drying the suspension to obtain Cu / CuO nanosheet bundle powder.

[0012] Among them, the reducing agents used are weak reducing agents such as sodium citrate, polyethylene glycol, and glucose. These reducing agents have hydroxyl groups on their tail structures. Under a reaction environment with a specific pH value and sufficient reaction time, they can uniformly grow nano-Cu / CuO along a specific direction, forming a nanosheet structure with uniform size. Moreover, the use of these weak reducing agents can regulate the relative content and ratio of CuO and Cu (not just a single nano-Cu) by optimizing the reaction conditions. Secondly, it can control the limited amount of Cu ions that are reduced, thereby controlling the reaction rate.

[0013] The molar ratio of the reducing agent to the copper salt is 1:2-6. When the molar ratio of the reducing agent to the copper salt is greater than 1:2, a large amount of Cu ions remains in the reaction solution, which causes waste of raw materials, and after the subsequent addition of sodium hydroxide solution, a large amount of copper hydroxide precipitate can be produced, which is mixed in the nano Cu / CuO powder, thereby reducing the purity of the product. When the molar ratio is less than 1:6, the purity of the nano Cu / CuO powder changes little with the increase of the concentration of the reducing agent, and too much reducing agent is also wasted. The macromolecular chain organic stabilizers such as polyvinylpyrrolidone, bovine serum albumin and polydimethyl diallyl ammonium chloride are used. The long hydrophobic carbon chains contained in these macromolecular chain organic stabilizers produce a large repulsive force, form a steric hindrance effect, effectively prevent the aggregation of nanoparticles, and reduce the size of the nano Cu or CuO. Meanwhile, the amine / amino part contained therein has a certain reducibility, which is conducive to improving the reduction rate. In addition, the selection of the above stabilizers also fully considers the concept of green chemistry, and the stabilizers are all non-toxic chemicals.

[0014] The pH value of the solution is adjusted to 13-14 by adding sodium hydroxide solution, in which the hydroxide ions and the copper ions in the copper salt form copper hydroxide precipitate, inhibit the massive ionization of the copper ions, promote the limited copper ions to be converted into copper atoms, and then are conducive to forming nano Cu / CuO with uniform size and small particle size. In combination with the conditions such as ultrasonic and subcooling drop, the obtained nano Cu / CuO has uniform size and small particle size.

[0015] The Cu / CuO nanosheet prepared by the technical scheme has uniform size and controllable morphology, can be rod-shaped, fibrous, flower-shaped or thorn-shaped, and has low cost and high yield.

[0016] As a further improvement of the application, the stepwise temperature rise is: rapidly rising to 50℃ at a rate of about 15℃ / min, and then slowly rising to 60-120℃ at a rate of 5-8℃ / min.

[0017] As a further improvement of the application, the temperature of the precursor solution A added dropwise is lower than 10℃.

[0018] As a further improvement of the application, when the reducing agent is sodium citrate, the molar ratio of sodium citrate to copper salt is 1:3.

[0019] As a further improvement of the application, the base is a solution such as sodium hydroxide solution and potassium hydroxide solution which can provide hydroxide ions.

[0020] As a further improvement of the present invention, in step S3, the superimposed ultrasound loading method is high-frequency pulse transverse loading. This technical solution leverages the acoustic streaming effect of ultrasound and the transverse micromechanical vibration. The transverse wave vibration can quickly reach the arc-shaped thin walls on both sides of the reaction vessel, forming an acoustic gradient and laminar flow at the nonlinear boundary (the arc-shaped thin wall), significantly improving the reaction rate and product yield.

[0021] More preferably, the ultrasonic frequency is 40-60kHz and the sound intensity is less than 5W / cm 2 Appropriate ultrasonic frequency and intensity can form a strong shock wave by means of the acoustic cavitation effect, generating a large number of tiny cavitation bubbles, and using these cavitation bubbles as nucleation points, significantly reducing the reaction activation energy and promoting the formation of tiny Cu or CuO nanosheet bundles; excessive frequency and intensity will destroy the original structure and original morphology of the synthesized nano-Cu / CuO.

[0022] More preferably, each pulse is loaded with ultrasound for 1 to 2 seconds and idle for 2 to 4 seconds. The loading time should not exceed 20 minutes continuously, as excessive continuous loading time can easily damage the ultrasound head.

[0023] As a further improvement of the present invention, in step S1, the copper salt is a mixture of one or both of copper acetate and copper ethylene acetonate; and in precursor solution A, the molar concentration of the copper salt is 0.05 to 0.2 mol / L. With this technical solution, the ligand structure formed by the Cu-O in copper acetate and copper ethylene acetonate provides excellent chemical stability, suppressing the ionization rate of Cu ions during the reaction, thereby controlling the nucleation and growth rate of Cu atoms. Furthermore, the size and morphology of the nano-Cu / CuO can be further controlled by combining the reaction conditions.

[0024] As a further improvement to the present invention, in step S3, the temperature is raised to 60-80°C in a stepwise manner. To increase the specific surface area of ​​the nano-Cu / CuO and achieve higher catalytic activity, it is often necessary to produce a higher content of flower-shaped CuO. In step S3, the optimal reaction temperature can be controlled based on the desired relative yields of nano-Cu and CuO. This technical solution, using a slow, stepwise temperature increase and maintaining a low reaction temperature, can promote the growth of a large number of CuO nanosheets.

[0025] As a further improvement of the present invention, the dropwise addition rate of the precursor solution A is 0.5 to 0.8 mL / min. Using this technical solution, adding a copper salt below 15°C to the reaction solution can increase the number of non-uniform nucleation sites for Cu or CuO clusters, promote large-area rapid nucleation of Cu or CuO clusters, thereby reducing the particle size of nano-Cu or CuO and improving uniformity.

[0026] As a further improvement of the present invention, the particle size of Cu or CuO can be controlled by using a droplet addition rate of 0.5 to 0.8 mL / min. A higher droplet addition rate will cause a large number of Cu or CuO clusters to aggregate in the solution, resulting in larger products (1 micron or even tens of microns), which is not conducive to leveraging the high surface energy advantage of nanoscale materials.

[0027] As a further improvement of the present invention, a double-layer burette is used, wherein the outer layer is passed through with ice salt water, and the inner layer is used for controllable dripping of copper salt. Furthermore, a rubber sleeve is coated between the two layers.

[0028] As a further improvement of the present invention, the mass concentration of the aqueous solution of the macromolecular chain organic stabilizer is 2-8.5 g / L. Controlling the mass concentration of these stabilizers to 2-8.5 g / L before adding them to Solution C allows for better control of particle size and morphology. When the mass concentration is too low, the stabilizer's coating and barrier effect is poor, resulting in less uniform particle size. When the mass concentration is too high, the stabilizers bridge and aggregate, providing only a limited coating effect and reducing size uniformity.

[0029] As a further improvement of the present invention, the macromolecular chain organic stabilizer is polyvinyl pyrrolidone. Further preferably, the quality grade of the polyvinyl pyrrolidone is K30, and the relative molecular mass is 30,000 to 40,000.

[0030] As a further improvement of the present invention, the cooling medium is ice water or ice salt water. The reaction process is an exothermic reaction, and an ice water bath or an ice salt water bath can cool the reaction solution to room temperature very quickly, quickly consume the residual heat in the reaction solution, and prevent the nanosheets from agglomerating.

[0031] As a further improvement of the present invention, in step S5, the suspension is ultrasonically dispersed for 5 minutes, then centrifuged, and deionized water and ethanol are added to the black-red precipitate for three centrifugal washings and ultrasonic dispersions. Furthermore, the cleaned black-red precipitate is finally immersed in ethanol for later use.

[0032] As a further improvement of the present invention, in step S5, the centrifugal speed is 2000-4000 rpm, and the centrifugation time is 12-15 minutes. In this technical solution, the size of the synthesized individual Cu or CuO nanosheet powders is approximately 100 nm, and the primary solvent is deionized water. Therefore, a moderate centrifugal speed and short centrifugation time can separate the nanosheet powders from the reaction solution.

[0033] As a further improvement of the present invention, in step S5, vacuum drying is performed at a temperature not exceeding 60°C to prevent oxidation of some of the resulting Cu nanosheet powder to CuO in air. Furthermore, preferably, the vacuum drying temperature is room temperature for 6 to 24 hours, and the product is stored at -5°C to -20°C.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] First, the technical solution of the present invention improves the traditional hydrothermal reduction process. After a short period of ultrasound + low-temperature hydrothermal reduction, the Cu / CuO nanosheet bundles with uniform size and controllable morphology are quickly (5 minutes) prepared at low temperature (as low as 60°C) with the help of acoustic cavitation effect and acoustic streaming effect. Nanosheets of various forms and structures can be formed, with a large specific surface area, which can give full play to the advantages of the nanostructure itself, showing high reaction catalytic activity and specific physical and chemical properties. The synthesis process is simple, the reaction conditions are low, and the cost is low. It is suitable for various fields such as catalytic decomposition, energy batteries, and electronic packaging materials.

[0036] Second, the entire reaction process of the technical solution of the present invention is carried out under low-temperature ultrasonic conditions. Compared with the complex synthesis process of the prior art, it avoids the harsh conditions of high temperature and high pressure, and does not require additional growth inducing agents. The reaction conditions are extremely low and the reaction rate is also high. At the same time, this method has strong selectivity and can well control the purity and relative content of Cu / CuO nanosheets, thus achieving low-cost, low-energy mass production of nano-Cu / CuO products. In addition, the short ultrasonic and low-temperature environment effectively reduces the corrosion and loss of the ultrasonic head in the reaction solution, reducing the frequency of ultrasonic head replacement and further reducing costs.

[0037] Third, the technical solution of the present invention uses water as a solvent, which on the one hand reduces the use of toxic organic solvents such as ethylene glycol and chloroform, and on the other hand improves the conversion rate and selectivity of the reduction reaction. At the same time, the solutes and stabilizers used are non-toxic or extremely low in toxicity, which prevents pollution while achieving effective utilization of resources and complies with the principles of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Scanning electron microscope / secondary electron microscope (SEM / SE) images of the mixed fibrous and flower-shaped Cu / CuO nanosheet bundles obtained in Example 1 of the present invention and magnified images of their local morphology; (a) low-magnification SEM / SE image, (b) magnified image of the local morphology;

[0039] Figure 2The SEM / SE images of the peony-shaped Cu / CuO nanosheet bundle obtained in Example 2 of the present invention and the magnified image of its local morphology; (a) low-magnification SEM / SE image, (b) magnified image of the local morphology;

[0040] Figure 3 The SEM / SE images of the chrysanthemum-shaped Cu / CuO nanosheet bundle obtained in Example 3 of the present invention and the magnified image of its local morphology; (a) low-magnification SEM / SE image, (b) magnified image of the local morphology;

[0041] Figure 4 SEM / SE images of the rod-shaped and thorn-shaped Cu / CuO nanosheet bundles obtained in Example 4 of the present invention and their local morphology magnifications; (a) low-magnification SEM / SE image, (b) local morphology magnification;

[0042] Figure 5 This is the energy dispersive spectrometer (EDS) surface scanning element distribution map of the peony-shaped Cu / CuO nanosheet bundle obtained in Example 2 of the present invention;

[0043] Figure 6 This is the X-ray diffraction (XRD) spectrum of the peony-shaped Cu / CuO nanosheet bundle obtained in Example 2 of the present invention.

[0044] Figure 7 The following are comparison photos of the solutions after ultrasonic reaction of Example 1 of the present invention and Comparative Examples 1 and 2; among them, a and b are Comparative Example 1, c and d are Example 1, and e and f are Comparative Example 2.

[0045] Figure 8 This is a picture after adding sodium hydroxide in step S6 of comparative example 3 of the present invention. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present invention are described in further detail below.

[0047] Example 1

[0048] This embodiment provides a method for preparing Cu / CuO nanosheets by hydrothermal reduction, comprising the following steps:

[0049] S1. Dissolve 1.04 g of copper acetate monohydrate in 100 mL of deionized water and stir magnetically at room temperature for 20 min to prepare precursor solution A.

[0050] S2. Dissolve 2.95 g of sodium citrate in 100 mL of deionized water to prepare solution B;

[0051] S3. Under magnetic stirring, heat solution B in an oil bath in a stepwise manner to 60-80°C and allow to stand for 5 minutes. Precursor solution A at 15°C is then added dropwise to solution B using a conventional burette at a rate of 0.8 mL / min. After the addition is complete, react for 30 minutes and stir to obtain a light blue solution C. The stepwise heating method involves rapidly heating the temperature to 50°C at a rate of approximately 15°C / min and then slowly heating the temperature to 60-80°C at a rate of 5-8°C / min. This stepwise heating method and low-temperature reaction conditions are more conducive to maintaining the dimensional uniformity and stability of the reaction product.

[0052] S4. Dissolve 4.02 g of sodium hydroxide in 100 mL of deionized water to prepare solution D;

[0053] S5. 0.21 g of polyvinyl pyrrolidone was dissolved in 100 mL of deionized water to prepare solution E, which inhibited the aggregation of nano-Cu / CuO by steric hindrance.

[0054] S6. Solution D was added to solution C to adjust the pH of the solution to 13, and solution E was quickly added to obtain a dark blue solution F. The strongly alkaline environment provides abundant hydroxide ions, which react with the Cu ions in the solution to form insoluble copper hydroxide. The copper hydroxide is then slowly ionized under the action of ultrasound and undergoes a reduction reaction to produce fine-sized nano-Cu / CuO.

[0055] S7. Solution F was maintained at 60-80°C and subjected to high-frequency pulsed transverse ultrasonic reaction for 5 min. The ultrasonic frequency was 40 kHz and the ultrasonic intensity was 0.6-0.84 W / cm 2 Under each pulse, ultrasound was applied for 1 s and then left blank for 2 s. Solution F quickly changed from dark blue to dark red. After cooling to room temperature in an ice-water bath, a dark red suspension G was obtained.

[0056] S8. The suspension G was ultrasonically dispersed for 10 min, centrifuged at 3000 r / min for 15 min, the supernatant was poured out, and deionized water and ethanol were added to the lower layer of black-red precipitate and washed and ultrasonically dispersed three times by centrifugation. Finally, the cleaned black-red precipitate was immersed in ethanol for use;

[0057] S9. After vacuum drying at room temperature for 6 h, the Cu / CuO nanosheet bundle powder can be obtained and stored at -5 to -20°C.

[0058] The preparation method of this embodiment is to apply ultrasound for a short time (5 minutes) + low temperature (60 ° C) hydrothermal reduction method, and use the acoustic cavitation effect, acoustic streaming effect and other effects to quickly prepare fibrous and flower-shaped mixed Cu / CuO nanosheets at low temperature. The average length of a single sheet is 150nm. Figure 1However, due to the combined effects of low reaction temperature, low frequency, intensity and duration of ultrasound application, the size uniformity was poor, and the length of some fibrous sheet bundles exceeded 700 nm.

[0059] Despite this, compared to the complex synthesis processes of existing technologies, the resulting sheet bundles still possess a large specific surface area and surface activity. They also avoid the harsh conditions of high temperature and pressure, requiring extremely low reaction conditions, thus reducing production costs. Furthermore, the use of water as a solvent reduces the use of toxic organic solvents such as ethylene glycol and chloroform, while also improving the conversion rate and selectivity of the reduction reaction, meeting the requirements of green chemistry. This method can be used to synthesize low-cost, high-surface-energy Cu / CuO nanosheet bundles.

[0060] Example 2

[0061] This example provides another method for preparing Cu / CuO nanosheets by hydrothermal reduction. Based on Example 1, this example differs from Example 1 in that:

[0062] In step S3, the precursor solution A was added dropwise to the supercooled solution B (7-9° C.) using a homemade double-layer burette. The temperature in the burette was measured to be 7-9° C., and the addition speed was 0.8 mL / min.

[0063] In step S5, the mass concentration of polyvinyl pyrrolidone in solution E is increased to 4.4 g / L. The specific steps are as follows: 0.44 g of polyvinyl pyrrolidone is dissolved in 100 mL of deionized water to prepare solution E.

[0064] In step S7, the ultrasonic frequency of the applied ultrasound is 60kHz and the ultrasonic intensity is 1.4-2W / cm 2 .

[0065] The method of this embodiment also rapidly prepared peony-shaped Cu / CuO nanosheet bundles at low temperature by briefly applying ultrasound. However, based on the specific embodiment 1, the mass concentration of the stabilizer, the ultrasound frequency, and the ultrasound intensity were increased. Through the stronger steric hindrance effect and the ultrasonic cavitation effect, the size uniformity of the Cu / CuO nanosheet bundles was significantly improved, and the size of the nanosheets was reduced. Figure 2 As shown in the figure, the uniformity and dispersion of the peony-shaped Cu / CuO nanosheet bundles are relatively good. The overall size of the flower is about 600 nm, and the average length of a single sheet bundle is less than 100 nm, showing a high specific surface area. Figure 5 and Figure 6 The corresponding elemental composition and phase of the nanosheet bundles are shown. The method also has high synthesis efficiency and product yield, fully meeting the synthesis needs of low-cost, large-scale and green chemistry.

[0066] Example 3

[0067] This example provides another method for preparing Cu / CuO nanosheets by hydrothermal reduction. Based on Example 2, this example differs from Example 2 in that:

[0068] In step S5, the mass concentration of polyvinyl pyrrolidone in solution E is increased to 8.1 g / L. Specifically, 0.81 g of polyvinyl pyrrolidone is dissolved in 100 mL of deionized water to prepare solution E.

[0069] In step S7, the ultrasonic frequency of the applied ultrasound is 60kHz and the ultrasonic intensity is 3.4-4.4W / cm 2 .

[0070] This embodiment further increases the mass concentration of the stabilizer, the ultrasonic frequency and the ultrasonic intensity on the basis of the specific embodiment 1, and quickly prepares the chrysanthemum-shaped Cu / CuO nanosheet bundles at low temperature, and the average size of a single sheet bundle is further reduced, as shown in FIG. Figure 3 However, due to the high-frequency and high-intensity ultrasound, more polyvinylpyrrolidone preferentially polymerizes, preventing a good coating effect, resulting in a decrease in the size uniformity and stability of the nanosheet bundles. Taking into account the effects of reaction concentration and ultrasound process parameters, this method can be used to synthesize low-cost, high-surface-energy Cu / CuO nanosheet bundles.

[0071] Example 4

[0072] This example provides another method for preparing Cu / CuO nanosheets by hydrothermal reduction. Based on Example 1, this example differs from Examples 1, 2, and 3 in that:

[0073] In step S3, the precursor solution A is supercooled and added dropwise to the solution B using a homemade double-layer burette. The temperature in the burette is measured to be 5-8° C., and the addition speed is 0.5 mL / min.

[0074] In step S7, the solution F is maintained at 60-80°C and subjected to high-frequency pulse transverse ultrasonic reaction for 10 minutes, with an ultrasonic frequency of 60 kHz and an ultrasonic intensity of less than 0.2 W / cm 2 .

[0075] The method of this embodiment can quickly prepare uniform-sized rod-shaped and thorn-shaped mixed Cu / CuO nanosheets at low temperature. Figure 4As shown, from the morphology, there are a large number of small thorns similar to secondary dendrites on the surface of the nanosheet. The supercooling dropwise addition of suitable temperature in the present embodiment can increase the non-uniform nucleation site, thereby promoting large-scale rapid nucleation, ensuring the small size and high uniformity of the synthesized nano Cu or CuO. At the same time, higher supercooling will cause the nano Cu or CuO clusters to grow along a specific direction during the conversion into nanosheets, thereby forming a rod-shaped and thorn-shaped mixed Cu or CuO nanosheet. The high-frequency, low-intensity, long-term ultrasonic action makes this morphology stably inherited (thorn-like structure is not destroyed). These thorn-like structures are used in fields such as chemical catalysis in addition to having a higher specific surface area. It is also expected to achieve good physical properties such as high strength and high electrochemical properties by means of mechanical interlocking or embedding, thereby widening its range of application.

[0076] Example 5

[0077] This embodiment provides another method for preparing Cu / CuO nanosheets by hydrothermal reduction. Based on Example 1, this embodiment differs from Example 1 mainly in the following steps:

[0078] S1. Dissolve 3.14 g of copper vinyl acetonate in 100 mL of deionized water and stir magnetically at 60°C for 30 min to prepare precursor solution A. Because copper vinyl acetonate is poorly soluble in water, solution A is effectively a suspension. This insoluble copper vinyl acetonate allows for limited release of Cu ions in subsequent reactions, thereby forming smaller nanosheet bundles.

[0079] S2. 6.19 g of sodium citrate and 3.6 g of glucose were dissolved in 100 mL of deionized water to prepare solution B; mixing the two reducing agents can reduce the required reaction time;

[0080] S3. Heat solution B in an oil bath in a stepwise manner to 120°C under magnetic stirring and allow to stand for 5 minutes. Add precursor solution A dropwise to solution B using a supercooled burette at a rate of 0.5 mL / min. After the addition is complete, react for 40 minutes and stir to obtain a light blue solution C.

[0081] S4. Adjust the pH of solution C to 13, dissolve 0.32 g of polyvinylpyrrolidone and 0.12 g of polydimethyldiallyl ammonium chloride in 100 mL of deionized water to prepare solution E. Use a co-stabilizer to reduce the size of the nano-Cu / CuO and promote its rapid sedimentation through the steric hindrance effect of the long carbon chain in polyvinylpyrrolidone and the electrostatic attraction of the quaternary ammonium salt groups in polydimethyldiallyl ammonium chloride.

[0082] S5. Solution E is quickly added to solution C to obtain a dark blue solution F;

[0083] S6. Solution F was maintained at 120°C and subjected to high-frequency pulsed transverse ultrasonic reaction for 30 min at an ultrasonic frequency of 60 kHz and an ultrasonic intensity of 2 to 2.4 W / cm 2 Under each pulse, ultrasound was applied for 1 s and then left blank for 2 s. Solution F quickly changed from dark blue to dark red. After cooling to room temperature in an ice-water bath, a dark red suspension G was obtained.

[0084] S8. After the suspension G was ultrasonically dispersed and centrifuged, the supernatant was poured out, and deionized water and ethanol were added to the lower layer of black-red precipitate and washed three times by centrifugation and ultrasonic dispersion. Finally, the clean black-red precipitate was immersed in ethanol for use;

[0085] S9. After vacuum drying, the Cu nanosheet powder is obtained and stored at -5 to -20°C.

[0086] The preparation method of this example utilizes ultrasound and hydrothermal reduction to rapidly produce Cu nanosheets, leveraging acoustic cavitation, acoustic streaming, and a co-coating agent. The nanosheets are approximately 200 nm long and less than 40 nm thick, exhibiting good dimensional uniformity and dispersion. Their excellent mechanical and electrical properties hold great potential for applications in energy, batteries, and electronic packaging.

[0087] Example 6

[0088] This example provides another method for preparing Cu / CuO nanosheets by hydrothermal reduction. Based on Example 5, this example differs from Example 5 in that:

[0089] In step S2, 11.2 g of polyethylene glycol is dissolved in 100 mL of deionized water to prepare solution B; polyethylene glycol; polyethylene glycol itself has reducing and structure-directing properties and can synthesize fine one-dimensional nanomaterials.

[0090] Before step S4, a sodium hydroxide solution still needs to be prepared. The specific steps are as follows: 4.02 g of sodium hydroxide is dissolved in 100 mL of deionized water to prepare solution D. In step S4, 0.42 g of polyvinyl pyrrolidone is dissolved in 100 mL of deionized water to prepare solution E.

[0091] The method of this embodiment ultimately produces fibrous Cu nanosheet bundle powder, or Cu nanofibers, which have good straightness and uniformity, a linear dimension of less than 50 nm, and have application value in the fields of flexible electronic manufacturing and electronic packaging.

[0092] The above methods all involve briefly applying ultrasound followed by low-temperature hydrothermal reduction, rapidly producing uniform-sized, morphologically controllable Cu / CuO nanosheet bundles at low temperatures. Nanosheets of various forms and structures are formed, possessing a large specific surface area and fully leveraging the inherent advantages of the nanostructure, exhibiting high catalytic activity and specific physicochemical properties. At the same time, the harsh conditions of high temperature and high pressure are avoided, requiring extremely low reaction conditions, thus saving production costs. Furthermore, the use of water as a solvent reduces the use of toxic organic solvents such as ethylene glycol and chloroform, while also improving the conversion rate and selectivity of the reduction reaction and meeting the needs of green chemistry. This method can be used to synthesize low-cost, high-surface-energy Cu / CuO nanosheet bundles.

[0093] Comparative Example 1

[0094] On the basis of Examples 1 to 6, the frequency and intensity of ultrasound in this comparative example are different, mainly:

[0095] The ultrasonic frequency of high-frequency pulse ultrasound was 20 kHz and the ultrasonic intensity was 0.2 W / cm 2 (Ultra-low frequency and low intensity). Due to the ultra-low ultrasonic frequency and low intensity, the ultrasonic cavitation and acoustic streaming effects are weak. After 20 minutes of reaction, only a small amount of black nano-CuO is produced, and even no black nano-CuO can be seen at the bottom. It is unable to continue to reduce to generate nano-Cu. The final suspension is as follows: Figure 7 As shown in a and b, the solution is still blue, that is, the Cu ions are not completely reduced under the non-ultrasonic or ultra-low ultrasonic process. Figure 7 As shown in c and d (the situations in Examples 1 to 6 are the same, only the two tubes in Example 1 are listed for comparison), the solutions in Examples 1 to 6 with appropriate ultrasonic process parameters are transparent, and the bottom of the centrifuge tube is the generated nano-Cu / CuO powder.

[0096] Comparative Example 2

[0097] Based on Comparative Example 1, the difference of this comparative example is that the ultrasonic frequency of the high-frequency pulse ultrasound is 70kHz and the ultrasonic intensity is 5W / cm 2 (Ultra-high frequency and high intensity). Since conventional ultrasonic generators cannot achieve frequencies exceeding 60kHz, we place the reaction vessel in a large steel tank filled with water, insert a large transducer directly into the water in the steel tank to apply ultra-high frequency ultrasound, and then place the reacted solution into a centrifuge tube. Figure 7 As shown in e and f on the right side of the figure, the obtained reaction product is the same as that in Example ( Figure 7 There is little difference between c) and d). The excessively high frequency and intensity here do not further refine the powder size or improve the surface properties. Instead, they further increase production costs (large transducers, ultrasonic generators, and other components, and consider their maintenance) and reduce production efficiency.

[0098] In summary, Comparative Example 1 and Comparative Example 2 did not achieve the desired low cost, high efficiency, and uniform small size.

[0099] Comparative Example 3

[0100] Based on Example 2, the difference in this comparative example is that the dropping speed is 5 mL / min, and after the reaction in step S3, the copper ions nucleate and grow immediately after adsorption, then after adding sodium hydroxide in step S6, flocculent substances appear, as shown in Figure 8 Finally, the desired product is not obtained. Ultimately, the particle size becomes large, and contains impurities such as copper hydroxide.

[0101] The above is a further detailed description of the present application in combination with specific preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing Cu / CuO nanosheets by hydrothermal reduction, characterized in that: The steps include: Step S1, dissolving copper salt in water to prepare precursor solution A; Step S2, dissolving a reducing agent in water to prepare solution B; the reducing agent is one or a mixture of two or more of sodium citrate, polyethylene glycol, and glucose; Step S3, stirring solution B, stepwise heating to 60-120°C, adding precursor solution A dropwise, and reacting for 20-40 minutes to obtain solution C; wherein the molar ratio of the reducing agent to the copper salt is 1:2-6, and the temperature of the precursor solution A is lower than 15°C; the stepwise heating refers to first rapidly heating to 50°C at a heating rate of not less than 12°C / min, and then slowly heating to the reaction temperature of 60-120°C at a heating rate of not more than 8°C / min; Step S4, adding alkali to solution C to adjust the pH of the solution to 13-14, then adding an aqueous solution of a macromolecular chain organic stabilizer to obtain a dark blue mixed solution, superimposing an ultrasonic reaction on the mixed solution at 60-120° C. for 5-30 minutes; when the mixed solution turns dark red, placing it in a cooling medium or a cooling environment and rapidly cooling it to room temperature to obtain a suspension; wherein the macromolecular chain organic stabilizer is one or a mixture of two or more of polyvinyl pyrrolidone, bovine serum albumin, and polydimethyldiallyl ammonium chloride; Step S5, separating, washing, and drying the suspension to obtain Cu / CuO nanosheet powder; In step S4, the superimposed ultrasound loading method is high-frequency pulse transverse loading, the ultrasound frequency is 40-60kHz, and the sound intensity is less than 5W / cm 2 Each pulse is loaded with ultrasound for 1~2s and idle for 2~4s.

2. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 1, characterized in that: In step S1, the copper salt is copper acetate; in the precursor solution A, the molar concentration of the copper salt is 0.05-0.2 mol / L.

3. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 1, wherein: In step S3, the temperature is raised to 60-80° C. in a stepwise manner; the precursor solution A is added dropwise at a rate of 0.5-0.8 mL / min.

4. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 1, wherein: The mass concentration of the macromolecular chain organic stabilizer aqueous solution is 2-8.5 g / L.

5. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 1, wherein: The cooling medium is ice water or ice brine.

6. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to any one of claims 1 to 5, characterized in that: In step S5, the suspension is ultrasonically dispersed for 5 minutes and then centrifuged. Deionized water and ethanol are added to the black-red precipitate to perform three centrifugal washings and three ultrasonic dispersions.

7. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 6, characterized in that: In step S5, the centrifugal speed is 2000-4000 r / min, and the centrifugal time is 12-15 min.

8. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 6, characterized in that: In step S5, vacuum drying is performed, and the temperature of the vacuum drying is not greater than 60°C.

9. The method for preparing Cu / CuO nanosheets by hydrothermal reduction according to claim 8, characterized in that: The vacuum drying temperature is room temperature and the time is 6 to 24 hours.

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