Vertical copper nanowire and preparation method and application thereof

Abstract

The invention discloses a vertical copper nanowire and a preparation method and application thereof, and belongs to the technical field of copper nanowire materials and preparation thereof. The method solves the problem that the copper nano array prepared by the existing method is easy to agglomerate. According to the preparation method disclosed by the invention, vertical growth, high dispersion, zigzag surface appearance and twin crystal structure formation of the copper nanowires are realized by accurately controlling electrodeposition conditions and template design in combination with a key freeze-drying post-treatment process, the active area and appearance orderliness of the copper nanowires are remarkably improved, and the preparation method is suitable for industrial production. Abundant active sites are provided for adsorption and reduction of nitrate radicals, so that the performance of the composite material in application such as electro-catalysis is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a vertical copper nanowire and its preparation method and application, belonging to the technical field of copper nanowire materials and their preparation. Background Art

[0002] One-dimensional nanomaterials have shown broad application prospects in many fields due to their unique physical and chemical properties. Among them, copper nanowires have received extensive attention in the fields of energy storage, photoelectrocatalysis, sensors, etc. due to their excellent electrical, optical, and catalytic properties.

[0003] Template electrodeposition is one of the common techniques for preparing one-dimensional nanomaterials. It restricts the growth direction and size of nanomaterials by using a template with a regular pore structure, thereby achieving the preparation of highly ordered nanoarrays. Porous anodic aluminum oxide (AAO) templates have become ideal template materials for preparing nanowire and nanorod arrays due to their highly ordered nanopore structure, adjustable pore diameter, and pore spacing. In the prior art, although certain progress has been made in the preparation methods of copper nanowire arrays, most of the prepared copper nanowires have a smooth surface and lack sufficient active sites, which limits their performance in applications such as electrocatalysis. Moreover, when preparing copper nanorods by traditional template electrodeposition, the nanorods agglomerate, resulting in poor dispersibility, small active area, and difficulty in achieving the vertical growth and uniform distribution of nanorods. In addition, the crystal structure of copper nanowires also has an important impact on their performance. Copper nanowires with twin crystal particles can exhibit more excellent electrical and catalytic properties.

[0004] In order to optimize the performance of copper nanorods prepared by template electrodeposition, researchers often try to regulate electrodeposition parameters to improve the surface morphology characteristics and specific surface area of nanorods. For example, by optimizing the pretreatment process of the template, the uniformity and conductivity of the template pores are improved, thereby achieving the uniform growth of copper nanorods. However, this method has high requirements for the template preparation process and is difficult to completely solve the problem of nanorod agglomeration. Although regulating electrodeposition parameters and optimizing the template pretreatment process can improve the dispersibility and specific surface area of nanowires to a certain extent, the existing preparation methods still have not completely solved the agglomeration problem. Especially in the drying process, the commonly used methods in this field, such as blowing air heating drying or natural drying after etching the template and cleaning, ignore the surface tension brought by water evaporation. This surface tension will cause copper nanowires to agglomerate, making it impossible to effectively improve the agglomeration phenomenon of copper nanowires even through the optimization of deposition parameters. Furthermore, the surface structure and electrochemical performance of copper nanowires will also be affected. Therefore, how to maintain the vertical growth and uniform dispersion of copper nanorods after etching the porous alumina template, while adjusting their crystal structure, increasing the active surface area, and reducing the ion transport resistance, is the key issue in current research. Summary of the Invention

[0005] The present invention aims to solve the problem that the copper nanoarrays prepared by existing methods are prone to aggregation, and provides a vertical copper nanowire, a preparation method thereof and an application thereof.

[0006] The technical solution of the present invention:

[0007] One of the objectives of the present invention is to provide a method for preparing a vertical copper nanowire, which method comprises the following steps:

[0008] (1) Depositing copper nanowires on a template of a substrate by using a two-electrode electrodeposition system, and removing the template after the deposition is completed to obtain a copper nanorod array;

[0009] (2) Immediately placing the copper nanorod array obtained in (1) into a freeze dryer for freeze-drying treatment to obtain highly dispersed copper nanowires perpendicular to the substrate.

[0010] Further defined, in (1), the substrate is a copper plate and the template is a porous anodic alumina.

[0011] More specifically defined, the center distance between the pores of the porous anodic alumina is 450 nm and the pore diameter is 140 nm.

[0012] Further defined, in the two-electrode electrodeposition system of (1), the substrate with the template is the cathode, and a brass plate is used as the anode, and the electrodeposition solution is composed of CuSO4, H2SO4 and H3BO3.

[0013] More specifically defined, the concentration of CuSO4 in the electrodeposition solution is 0.4 mol / L, the concentration of H2SO4 is 0.1 mol / L, and the concentration of H3BO3 is 10 g / L.

[0014] Further defined, in (1), the deposition temperature is 40 °C, the voltage is 0.4 - 0.5 V, and the time is 15 min.

[0015] Further defined, the process of removing the template in (1) is: soaking in a 5% NaOH solution at 40 °C for 20 min.

[0016] Further defined, the freeze-drying treatment conditions in (2) are: freeze-drying at 10 -3 Pa and -70 °C for 24 h.

[0017] Another objective of the present invention is to provide a vertical copper nanowire array prepared by the above method, specifically, the copper nanorod array is highly dispersed and perpendicular to the substrate.

[0018] Another objective of the present invention is to provide an application of the above vertical copper nanowire array, specifically for energy storage, photoelectrocatalysis and sensor preparation.

[0019] Advantageous effects:

[0020] Through precise control of electrodeposition conditions and template design, combined with the key freeze-drying post-treatment process, the present invention realizes the vertical growth, high dispersion, serrated surface morphology and formation of twin crystal structures of copper nanowires, significantly improving the active area and morphological orderliness of copper nanowires. The present invention utilizes freeze-drying technology to effectively avoid the generation of surface tension during the water evaporation process, preventing the nanowires from bending or aggregating due to capillary forces, thus completely retaining their vertical arrangement characteristics and high dispersion. Moreover, the serrated surface significantly increases the specific surface area of copper nanowires, exposing more highly active crystal planes of (110) and (111), providing abundant active sites for nitrate adsorption and reduction, thereby significantly improving their performance in applications such as electrocatalysis. At the same time, the internal twin structure optimizes the electron transport path, reduces the charge transfer resistance, and enhances the adsorption stability of key intermediates by introducing lattice defects (such as twin boundaries). In addition, the preparation method provided by the present invention has the advantages of simple operation, low cost, good repeatability and suitability for large-scale production, and can be widely applied to fields such as energy storage, photoelectrocatalysis, sensors, etc., having important scientific significance and application value. Description of the Drawings

[0021] Figure 1 Top view of the copper nanowire array prepared in Comparative Example 1;

[0022] Figure 2 Top view of the copper nanowire arrays prepared in Comparative Example 2 and Example 2;

[0023] Figure 3 Enlarged top view of the copper nanowire arrays prepared in Examples 1-3;

[0024] Figure 4 XRD diffraction pattern of the copper nanowires prepared in Example 2;

[0025] Figure 5 Internal transmission electron micrograph of the copper nanowires prepared in Example 2;

[0026] Figure 6 Faraday efficiency and ammonia production rate of copper foil electrocatalysis;

[0027] Figure 7 Faraday efficiency and ammonia production rate of the copper nanowire array electrocatalysis prepared in Example 2;

[0028] Figure 8 Faraday efficiency and ammonia production rate of the copper nanowire array electrocatalysis prepared in Comparative Example 2. Detailed Description of the Invention

[0029] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the embodiments of the specification.

[0030] In the following description, numerous specific details are set forth to facilitate a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0031] Secondly, the so-called "one embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0032] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in this field, and those skilled in the art can obtain them through commercial channels without special instructions.

[0033] Example 1:

[0034] (I) Preparation of the substrate

[0035] Select a high-purity copper plate as the substrate support material. Use sandpaper to polish the surface of the copper plate to remove the surface oxide layer and impurities. Subsequently, immerse the copper plate in a 5% dilute sulfuric acid solution for 20 minutes to further remove the residual impurities on the surface. Polish the substrate copper foil, and ultrasonically clean the copper foil with ethanol and deionized water. Use the copper foil to coat the surface of the copper plate, and apply an insulating glue in the non-template area to prevent copper deposition in these areas, thereby ensuring that the copper nanorods grow only in the template area along the predetermined direction, improving the deposition efficiency of the electrodeposition process, and also ensuring the uniformity and perpendicularity of the copper nanorods. This control of the deposition position enables the copper nanorod array to grow highly uniformly within the template area, avoiding unnecessary deposition in the non-template area, thereby improving the preparation efficiency and overall performance of the material.

[0036] (II) Electrodeposition process

[0037] A porous anodic aluminum oxide (AAO) template with a center-to-center hole spacing of 450 nm and a pore diameter of 140 nm was selected as the growth template and placed in the template area of the substrate. A two-electrode electrodeposition system was used, with the polished brass plate as the anode and the substrate pretreated in step (I) as the cathode. By means of mechanical stress application, the cathode sheet, template, polytetrafluoroethylene aqueous microporous diaphragm, and anode sheet were tightly pressed together. This step is crucial for ensuring that copper ions uniformly enter the template cavities during electrodeposition, thereby controlling the morphology and arrangement of copper nanowires. Mechanical pressure helps eliminate the voids between the template and the substrate, ensuring sufficient contact between the electrolyte and the inner surface of the template pores, thus promoting the uniform deposition and vertical growth of copper nanowires. The electrodeposition solution consists of 0.4 mol / L CuSO4, 0.1 mol / L H2SO4, and 10 g / L H3BO3. Here, H2SO4 increases the conductivity of the electrodeposition solution, and H3BO3 acts as a complexing agent, helping to control the reduction rate and deposition behavior of copper ions, thereby affecting the morphology of copper nanowires.

[0038] During electrodeposition, the electrolyte was heated to 40 °C in a constant-temperature water bath. The appropriate temperature helps promote the migration and reduction of copper ions, optimize the reduction rate of copper ions and the growth rate of copper crystals, and also helps the directional growth and morphology control of copper nanowire crystals, forming copper nanowires with a serrated surface. Deposition was carried out at a deposition voltage of 0.2 V for 15 min to form a copper nanowire array perpendicular to the substrate.

[0039] (III) Removal of the AAO template

[0040] After electrodeposition, the cathode sheet was taken out of the electrodeposition system, rinsed with deionized water to remove the residual electrodeposition solution on the surface. Subsequently, the cathode sheet was placed in a 5% NaOH solution and soaked at 40 °C for 20 min to completely remove the AAO template, releasing a dispersed copper nanorod array.

[0041] (IV) Drying treatment

[0042] The copper nanowire array after removing the AAO template was rinsed with a large amount of deionized water to thoroughly remove the residual etching solution on the surface, and then immediately placed in a freeze dryer. The vacuum was pumped to 10 -3 Pa, and freeze-dried at -70 °C for 24 h to obtain a highly dispersed copper nanowire array perpendicular to the substrate.

[0043] Example 2:

[0044] The difference between this example and Example 1 is that in step (II), deposition was carried out at a deposition voltage of 0.4 V for 15 min to form a copper nanowire array perpendicular to the substrate, and the remaining process steps and parameter settings are the same as those in Example 1.

[0045] Example 3:

[0046] The difference between this example and the previous example lies in that: in (2), deposition is carried out at a deposition voltage of 0.6 V for 15 min to form a copper nanowire array perpendicular to the substrate, and the remaining process steps and parameter settings are the same as those in Example 1.

[0047] Comparative Example 1:

[0048] The difference between this comparative example and Example 2 is that: in (4), the copper nanowire array after removing the AAO template is rinsed with a large amount of deionized water to thoroughly remove the corrosive liquid remaining on the surface, and then dried under a blowing and drying condition at a specific temperature of 60 °C for 15 min to obtain a copper nanowire array.

[0049] Comparative Example 2:

[0050] The difference between this comparative example and Example 2 is that: in (4), the copper nanowire array after removing the AAO template is rinsed with a large amount of deionized water to thoroughly remove the corrosive liquid remaining on the surface, left standing for 20 min, and then placed in a freeze dryer, evacuated to 10 - 3 Pa, and freeze-dried at -70 °C for 24 h to obtain a copper nanowire array.

[0051] Effect Example:

[0052] (1) The top views of the copper nanowire arrays prepared in Example 2 and Comparative Examples 1-2 were characterized, and the results are as shown in Figure 1 and Figure 2 shown. Among them, Figure 1 is the top view of the copper nanowire array prepared in Comparative Example 1. It can be seen from the figure that under the blowing and drying condition, the tops of the copper nanowires adsorb and aggregate with each other to form clusters, seriously damaging their ordered array structure. This is mainly due to the rapid evaporation of water, which causes the surface energy of the copper nanowires to increase rapidly, resulting in the adsorption and aggregation of the tops of the copper nanowires with each other to form clusters. At this time, only the tops of the copper nanowires in the middle of the nanoclusters are exposed, and the sides with high catalytic activity are shielded, resulting in most active sites being unable to effectively participate in the reaction, thereby significantly reducing the catalytic performance of the material. Figure 2 In (a) is the top view of the copper nanowire array prepared in Comparative Example 2. It can be seen from the figure that due to partial evaporation of water during the waiting period, even though freeze-drying is carried out subsequently, the aggregation phenomenon is greatly improved, but there is still a certain degree of aggregation of the copper nanowires. Figure 2Figure (b) is the top view of the copper nanowire array prepared in Example 2. It can be seen from the figure that the copper nanowires are distributed in an ordered array on the entire substrate surface. The distribution between the nanowires is uniform, without obvious aggregation or vacancy, and the height is consistent, which confirms the dispersion and uniformity of the prepared nanowires. This indicates the effective control of the instant freeze-drying on the nanowire distribution during the preparation process. This vertical and dispersed morphology can provide a direct and efficient electron transport path, thereby reducing the electron transport resistance and increasing the conductivity. At the same time, the dispersed nanowire array increases the contact area between the material and the electrolyte, providing more active sites for the electrochemical reaction, which helps to improve the reaction rate and efficiency.

[0053] (2) Figure 3 Figure (a) is the enlarged SEM image of the top of the copper nanowire array prepared in Example 1-3. Among them, (a) is the enlarged SEM image of the top of the copper nanowire array obtained in Example 1. It can be seen from the figure that the surface and tip of the obtained copper nanowires are relatively smooth. Among them, (b) is the enlarged SEM image of the top of the copper nanowire array obtained in Example 2. It can be seen from the figure that the surface of the obtained copper nanowires is rough but relatively uniform. Among them, (c) is the enlarged SEM image of the top of the copper nanowire array obtained in Example 3. It can be seen from the figure that the deposition uniformity is very poor. This is because too large deposition voltage will cause non-uniform deposition of copper nanowires, and too small voltage may lead to too short nanowire length. Therefore, the selection of deposition voltage plays an important role in the morphology of copper nanowires. At a deposition voltage of 0.4V, tiny protrusions and depressions are formed on the surface of the nanowires, forming a unique serrated surface morphology. This structure significantly increases the specific surface area of the nanowires and provides more active sites.

[0054] (3) Figure 4 Figure is the XRD pattern of the copper nanowires prepared in Example 2. It can be seen from the figure that the orientations of the deposited copper are (111), (200), (220), (311), (420). By comparing the ratio of the diffraction peaks of each crystal orientation with the standard card, the exposure ratio of the (110) crystal plane of the copper nanowires increases, indicating the existence of preferred orientation during the growth of the copper nanowires. The crystal in the copper nanowires is a face-centered cubic crystal system, with lattice constants a = b = c = 3.615, and the grain size is about 86.5nm.

[0055] (4) Figure 5High-resolution transmission electron microscopy image of the copper nanowires prepared in Example 2, where (a) reflects that the copper nanowires have different crystal orientations. In addition to the close-packed plane (111), there is also the (110) plane, which is consistent with the XRD results. It can be seen from Figure (b) that the internal structure of the copper nanowires is a twin crystal, and twin boundaries are commonly present. The twin crystal structure significantly improves the electrocatalytic performance of the copper nanowire array by exposing high-active sites, optimizing electron transport, and enhancing stability. The diffraction pattern of the copper nanowires in Figure (c) further illustrates the twin crystal structure of the copper nanowire crystals.

[0056] (5) Using the copper foil and the copper nanowire array prepared in Example 2 as the working electrodes, a Pt sheet electrode as the auxiliary electrode, and Hg / HgO (1 mol / L KCl aqueous solution) as the reference electrode, a three-electrode system was constructed in an H-cell electrolytic cell with a 1 mol / L KOH solution containing 500 ppm KNO3 to compare the effects of catalytic reduction of nitrate to ammonia. Among them Figure 6 Shows the effect of electrocatalytic reduction of nitrate to ammonia by the copper foil. The test voltage was -0.25 to -0.75 V vs. RHE. As can be seen from the figure, as the voltage increased, the ammonia production rate of the copper foil gradually increased, and the Faraday efficiency first increased and then decreased. At -0.45 V vs. RHE, the Faraday efficiency of the copper foil for reducing nitrate was the highest, but only 14%. Figure 7 Shows the effect of the copper nanowire array prepared in Example 2 for catalytic reduction of nitrate to ammonia. The test voltage was 0.05 to -0.45 V vs. RHE. As can be seen from the figure, as the voltage increased, the ammonia production rate of the copper foil increased, reached the maximum at -0.25 to -0.35 V and then decreased. The Faraday efficiency first increased and then decreased. At -0.15 V vs. RHE, the Faraday efficiency was 69%. Compared with the copper foil, the vertical zigzag copper nanowire array has a larger specific surface area and higher active sites, increasing the Faraday efficiency by 5 times. This shows that the vertical copper nanowire array with a zigzag surface and twin crystal structure not only greatly improves the Faraday efficiency of electrocatalytic reduction of nitrate, but also reduces the reduction potential of nitrate.

[0057] (6) Using the copper nanowire array prepared in Comparative Example 2 as the working electrode, a Pt sheet electrode as the auxiliary electrode, and Hg / HgO (1 mol / L KCl aqueous solution) as the reference electrode, an experiment on the catalytic reduction of nitrate to ammonia was carried out in a three-electrode system constructed with an H-cell electrolytic cell containing 1 mol / L KOH solution with 500 ppm KNO3. At -0.15 V vs. RHE, the Faraday efficiency of the agglomerated copper nanowires prepared in Comparative Example 2 for reducing nitrate was the highest, reaching 50.6%. The Faraday efficiency and ammonia yield of the agglomerated copper nanowire sample for reducing nitrate were both lower than those of the dispersed copper nanowire sample and higher than those of the blank copper foil sample. That is, although the nanowires increased the reaction active area, the agglomerated morphology restricted the ion transport on the material surface and could not exert the best catalytic effect of the copper nanowires, demonstrating the superiority of the dispersed copper nanowires in photoelectrocatalysis.

[0058] As described above, only the preferred specific embodiments of the present invention are provided. These specific embodiments are different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing vertical copper nanowires, characterized in that: include: (1) depositing copper nanowires on a template of a substrate using a dual-electrode electrodeposition system, and removing the template after the deposition is completed to obtain a copper nanorod array; (2) The copper nanorod array obtained in (1) is immediately placed in a freeze dryer for freeze drying to obtain highly dispersed copper nanowires that are perpendicular to the substrate.

2. The preparation method according to claim 1, characterized in that: (1) The substrate is a copper plate and the template is porous anodized aluminum.

3. The preparation method according to claim 2, characterized in that: The center distance between the porous anodized aluminum pores is 450nm and the pore diameter is 140nm.

4. The preparation method according to claim 1, characterized in that: In the two-electrode electrodeposition system of (1), the substrate with the template is the cathode, the brass plate is the anode, and the electrodeposition solution is composed of CuSO4, H2SO4 and H3BO3.

5. The preparation method according to claim 4, characterized in that: The concentration of CuSO4 in the electrodeposition solution is 0.4 mol / L, the concentration of H2SO4 is 0.1 mol / L, and the concentration of H3BO3 is 10 g / L.

6. The preparation method according to claim 1, characterized in that: (1) The deposition temperature is 40°C, the voltage is 0.4-0.5V, and the time is 15min.

7. The preparation method according to claim 1, characterized in that: (1) The template removal process is: using a 5% NaOH solution and soaking at 40°C for 20 minutes.

8. The preparation method according to claim 1, characterized in that: (2) The freeze-drying conditions are: - 3 Freeze-dry at -70 °C for 24 h.

9. A vertical copper nanowire array prepared by the method according to any one of claims 1 to 8, characterized in that: The copper nanorod arrays are highly dispersed and perpendicular to the substrate.

10. An application of the vertical copper nanowire array according to claim 9, characterized in that: Used for energy storage, photoelectrocatalysis and sensor preparation.

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