Preparation method and application of aluminum copper iron oxide nanosheet with ordered stripes on surface

Abstract

The application provides a preparation method and application of aluminum copper iron oxide nanosheet with ordered stripes on the surface, and belongs to the technical field of nanomaterial preparation, and comprises the following steps: aluminum, copper and iron elements are respectively proportioned according to atomic ratio, and alloy ingot is obtained through smelting; the obtained alloy ingot is subjected to annealing treatment in a furnace, is crushed and then sieved to obtain alloy powder; the alloy powder is put into a NaOH solution after the solution is preheated, and the alloy powder is reacted and heated at the same time; after the reaction is completed, the product is washed and then dried to obtain aluminum copper iron oxide nanosheet with ordered stripes on the surface, and the nanosheet and the composition unit of the stripe pattern on the surface of the nanosheet are both single crystal structures. The nanosheet has excellent nitrate electrocatalytic reduction ammonia production performance, and realizes high faradaic efficiency and yield.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface and their application. Background Technology

[0002] Regular, ordered patterns can bring about special functions and properties. Striped patterned materials, due to their periodic arrangement, tunable wettability, and geometric confinement effect, have been widely used in various fields such as sensing, biotemplating, and catalysis. Therefore, many scholars have devoted themselves to the efficient preparation and synthesis of striped patterns. In 2005, Huang et al. formed Langmuir-Blodgett films on liquid surfaces by inducing particles to form striped patterns on substrates using a dip-coating method (Huang et al, Nature Materials, 2005, 4, 896-900). Later, Cai et al. mixed nanoparticles and droplets, applied directional induced dehumidification conditions, and prepared circular striped patterns under the regular contraction of the droplet contact lines (Cai et al, Journal of the American Chemical Society, 2008, 130, 19, 6076-6077). Tu et al. also successfully fabricated striped patterns using electron beam lithography on special thin films, demonstrating high sensitivity in optical gas sensing (Tu et al, Nature Materials, 2021, 20, 93-99). Hu et al. prepared striped patterned hydrogels by combining multi-step sequential polymerization with photolithography, achieving both high strength and high toughness (Hu et al, Macromolecules, 2025, 58, 8, 3993-4000).

[0003] Currently, the design of the shape, crystal structure, and arrangement orientation of the building units in these prepared stripe patterns is still in its initial stage. Most building units are convex, and the crystal structures exhibit amorphous / polycrystalline characteristics. The design of the shape and crystal characteristics of the building units is of great significance for exploring their performance. For example, the special surface of concave shapes can bring more active sites in catalysis, and single-crystal structures have greater advantages in carrier mobility and conductivity due to the elimination of grain boundaries. However, there are almost no nanoscale stripe patterns composed of concave single-crystal building units that have been synthesized so far. The main reason is that the preparation of nanostripes with these ordered characteristics involves thermodynamic instabilities and the complexity of ordered dynamics.

[0004] Nanosheets, through lattice matching, are commonly used as matrices for the epitaxial growth of ordered arrays (Zhang et al, Nature Nanotechnology, 2022, 17, 493–499). However, due to the difficulty in precisely controlling nucleation sites, it is challenging for their building units to form complex stripe pattern arrays. Therefore, developing an efficient and inexpensive method to prepare ordered nanostripe patterns using nanosheets as a matrix has become an urgent problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on their surface. The aim is to solve the problem of preparing ordered nano-striped patterns in a cost-effective and efficient manner. The aluminum-copper-iron oxide nanosheets with ordered stripes prepared using the method provided by this invention exhibit excellent electrocatalytic reduction performance for ammonia production from nitrate.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0007] One objective of this invention is to provide a method for preparing aluminum-copper-iron oxide nanosheets with ordered striations on their surface, comprising the following steps:

[0008] S1. Aluminum, copper and iron elements are weighed according to atomic ratio and placed in a vacuum induction melting furnace for uniform melting to obtain alloy ingots;

[0009] S2. Anneal the alloy ingot obtained in step S1 in a furnace;

[0010] S3. After crushing the annealed alloy ingot obtained in step S2, the ingot is sieved to obtain alloy powder.

[0011] S4. After preheating the NaOH solution, put the alloy powder obtained in step S3 into the solution to react, and heat it at the same time during the reaction.

[0012] S5. After the reaction is complete, the product obtained in S4 is washed, and some moisture is retained before drying to obtain aluminum-copper-iron oxide nanosheets with ordered stripes on the surface.

[0013] Preferably, in step S1, the purity of the aluminum, copper, and iron elements is 99.99%, and the aluminum, copper, and iron are prepared in an atomic ratio of 63:25:12. Melting according to this atomic ratio allows the aluminum, copper, and iron to form a single quasicrystalline structure for subsequent hydrothermal reactions.

[0014] Preferably, in step S1, the melting temperature is 1700°C. In embodiments of the present invention, melting is performed more than 6 times to achieve uniform mixing of components, followed by natural cooling to obtain an alloy ingot.

[0015] Preferably, in step S2, the annealing temperature is 750°C and the annealing time is 2 hours. Annealing at this temperature can yield an alloy ingot with a single quasi-crystalline phase.

[0016] Preferably, in step S3, the target size for sieving the crushed alloy ingot is 200-300 mesh.

[0017] Preferably, in step S4, the concentration of the NaOH solution is 2-4 mol / L, more preferably 3 mol / L, the preheating temperature and reaction temperature are 75°C, and the reaction time is 5-7 hours.

[0018] Preferably, in step S5, the solid-liquid ratio of the product during drying is 1.5 g / mL. Retaining a certain amount of water in the product to be dried provides an environment for droplet evaporation to facilitate the formation of stripes on the nanosheet surface. The drying temperature range is from room temperature to 120°C.

[0019] A second objective of this invention is to provide aluminum-copper-iron oxide nanosheets with ordered stripes on their surface, prepared by the aforementioned method. By controlling the drying conditions, an ordered stripe pattern can be formed on the surface of the nanosheets. Furthermore, the stripe size on the nanosheet surface reaches the nanometer scale, and the stripe spacing is in the range of 80-130 nm.

[0020] The surface stripe pattern of the nanosheet can be composed of spherical, hexagonal snowflake-shaped, or irregularly concave nanoparticles. Among them, the hexagonal snowflake-shaped particles can maintain a uniform orientation on the surface of the nanosheet, exhibiting an ordered characteristic.

[0021] Preferably, the nanosheets and the constituent units of the stripe pattern on the nanosheet surface are all single-crystal structures with an Al composition. 14 Fe 24 Cu2O 60 The crystal structure is α-Fe₂O₃ rhombohedral type, space group [space group missing]. (167), JCPDS No. 33-0664. The applicant's research found that the original Al 63 Cu 25 Fe 12 The alloy is reacted with NaOH to obtain nanosheets, and stripes are formed on the surface of the nanosheets by drying in a water-containing atmosphere. The nanosheets and stripes are characterized by having the above-mentioned element ratio.

[0022] A third objective of this invention is to provide an application for the aluminum-copper-iron oxide nanosheets with ordered striations on their surface. When used in the electrocatalytic reduction of nitrate to ammonia, the highest Faraday efficiency of 91.23% and the highest yield of 13.42 mg / h were achieved at -0.5V (relative to the reversible hydrogen electrode). -1 cm-2 .

[0023] The stripe formation mechanism of this invention is: Al 63 Cu 25 Fe 12 Precursor powder undergoes dealloying and hydrothermal reactions in NaOH solution to form hexagonal nanosheets with smooth, stripe-free surfaces. When the product is subsequently dried, a certain amount of moisture remains, causing ions from the gaps between the nanosheets to escape into the aqueous solution upon heating. As the water evaporates, dispersed droplets with a certain ion concentration form on the flat nanosheet surface. Because the evaporation rate is higher at the droplet-nanofe-air three-phase contact line, the evaporation rate of water molecules is higher than inside the droplet, causing the ion concentration to reach supersaturation near the contact line first, resulting in the precipitation of a ring of crystal nuclei. The final shape of the crystal nuclei (e.g., spherical, hexagonal snowflake-like, irregular concave) is influenced by both the nanosheet lattice matching and the growth environment. As liquid is continuously lost at the contact line, the contact angle decreases. When a critical angle is reached, it becomes difficult to maintain the pinning behavior of the contact line, and the droplet contracts inward, leaving the first ring of stripes. During droplet contraction, the contact angle increases. When the critical contact angle is exceeded, a second pinning and crystal nucleus precipitation and growth occur, ultimately forming the second ring of stripes. By doing this, concentric stripe patterns eventually form on the surface of the nanosheets.

[0024] The beneficial effects and advantages of the present invention are as follows:

[0025] First, this invention does not rely excessively on equipment and complex processing techniques, and can easily, efficiently and cost-effectively prepare nanoscale stripe patterns.

[0026] Secondly, this preparation method combines the stick-slip motion of the droplet contact line with the lattice matching of the nanosheet matrix, which can realize the construction of single-crystal stripe patterns on the surface of two-dimensional nanosheets, providing a new approach for the preparation of nanofunctional materials.

[0027] Meanwhile, the constituent units of the nano-striped pattern can be not only spherical nanoparticles, but also more complex uniform hexagonal snowflake-shaped nanoparticles, and the hexagonal nanocrystals on the surface of the nanosheet can maintain a consistent orientation. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The image shown is a scanning electron microscope image of the sample obtained in Example 1. Figure 1 (a) uses a 5K magnification. Figure 1 (b) uses a 10K magnification. Figure 1 (c) uses a 30K magnification. Figure 1 The middle (d) uses a magnification of 150K;

[0030] Figure 2 The particle size distribution of the nanosheet surface stripe structure units of the sample obtained in Example 1 is shown in the diagram.

[0031] Figure 3 The image shows an electron microscope (EM) image of the nanosheets and hexagonal nanocrystals on the surface of the sample obtained in Example 1. Figure 3 Image (a) is a transmission electron microscope image. Figure 3 (b) is a selected area electron diffraction pattern. Figure 3 Image (c) is a high-resolution image. Figure 3 (d) to (g) are Fourier transform maps of different regions;

[0032] Figure 4 This is a high-angle annular dark-field transmission electron microscopy (TEM) image of the nanosheets and hexagonal nanocrystals on the surface of the sample obtained in Example 1. Figure 4 Image (a) is an electron microscope image. Figure 4 (b) is a distribution map of elements. Figure 4 Image (c) shows a line scan of the particles on the surface of the nanosheet. Figure 4 (d) represents the percentage of a specific component;

[0033] Figure 5 The conditions were the same as in Example 1, except that the drying conditions were changed to freeze drying. The scanning electron micrograph of the prepared sample is shown.

[0034] Figure 6 The results are from the electrocatalytic reduction of nitrate to ammonia using the sample obtained in Example 1 at different potentials. Figure 6 In the middle (a), Faraday efficiency is represented. Figure 6 (b) represents the yield;

[0035] Figure 7 This is a scanning electron microscope image of the stripe pattern on the surface of the sample in Example 2. Figure 7 Image (a) is taken at 30K magnification, showing the nanosheet morphology. Figure 7 (b) is a 150K magnification image showing the stripe morphology on the surface of the nanosheets;

[0036] Figure 8 This is a particle size distribution chart of the striped structural units in the sample of Example 2;

[0037] Figure 9 To present the experimental results of the electrocatalytic reduction of nitrate to ammonia for sample 2 under different potentials, Figure 9 In the middle (a), Faraday efficiency is represented. Figure 9 (b) represents the yield;

[0038] Figure 10 This is a scanning electron microscope image of the stripe pattern on the sample surface in Example 3. Figure 10 Image (a) is taken at 30K magnification, showing the nanosheet morphology. Figure 10 (b) is a 150K magnification image showing the stripe morphology on the surface of the nanosheets;

[0039] Figure 11 This is a particle size distribution chart of the surface pattern construction units of the sample in Example 3;

[0040] Figure 12 This is a scanning electron microscope image of the stripe pattern on the sample surface in Example 4. Figure 12 Image (a) is taken at 30K magnification, showing the nanosheet morphology. Figure 12 (b) is a 150K magnification image showing the stripe morphology on the surface of the nanosheets;

[0041] Figure 13 This is a particle size distribution chart of the stripe structure units on the sample surface of Example 4;

[0042] Figure 14 This is a scanning electron microscope image of the sample from Comparative Example 1. Figure 14 Image (a) is taken at 20K magnification, showing the nanosheet morphology. Figure 14 (b) is a 100K magnification image showing the surface morphology of the nanosheets;

[0043] Figure 15 The image shown is a scanning electron microscope image of sample 2 (Comparative Example). Figure 15 Image (a) is taken at 20K magnification, showing the nanosheet morphology. Figure 15 (b) is a 50K magnification image of the nanosheet surface morphology. Detailed Implementation

[0044] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface includes the following steps:

[0047] (1) Aluminum, copper and iron elements are mixed in an atomic ratio of 63:25:12 and uniformly melted in a vacuum induction melting furnace at a rated temperature of 1700℃. The mixture is melted more than 6 times to achieve uniform mixing of components and then naturally cooled to obtain alloy ingots.

[0048] (2) The obtained alloy ingot is annealed in a furnace at 750°C for 2 hours.

[0049] (3) The annealed alloy ingot is crushed and screened to obtain alloy powder with a mesh size of 200-300.

[0050] (4) After preheating the powder in a 3 mol / L NaOH solution at 75°C for half an hour, place the powder in the solution and react at 75°C for 6 hours.

[0051] (5) After the reaction is complete, the sample obtained from the reaction is washed 8 times with deionized water to remove waste liquid. The reaction and washed sample is placed on a heating plate at 90°C for drying. A certain amount of water is reserved in the sample, and the solid-liquid ratio is 1.5 g / mL. After complete drying, the sample is characterized by scanning electron microscopy and transmission electron microscopy.

[0052] Figure 1 Here are scanning electron microscope images of the samples obtained from the reaction. Figure 1 (a) and (b) use low magnification. Figure 1 (c) and (d) are taken at high magnification. It can be seen that at low magnification, the powder particles are composed of crisscrossing nanosheets; at high magnification, concentric stripe patterns are visible on the surface of the nanosheets, and the stripes are composed of hexagonal snowflake-like nanocrystals arranged in an orderly manner.

[0053] Figure 2 The image shows the particle size distribution of the structural units of the stripe pattern on the nanosheet surface of the sample. It can be seen that the particle size of the particles constituting the stripes is concentrated at 104.3 ± 6.3 nm, exhibiting extremely high size uniformity.

[0054] Figure 3 The images show electron microscope (EM) images of the nanosheets and hexagonal nanocrystals on the sample's surface. Figure 3 Image (a) is a transmission electron microscope image, showing the morphology of the particles that make up the stripes and... Figure 1 Consistent. Figure 3 (b) is the circled portion of (a), i.e., the selected area electron diffraction image of the nanocrystals forming stripes on the surface of the nanosheets. It shows a sharp set of single-crystal spots, which can be identified as rhombohedral α-Fe2O3, corresponding to the (110) crystal plane under the

[001] zone axis, and its space group is (167), the standard card number is JCPDS No. 33-0664. Figure 3 Image (c) is a high-resolution image. Figure 3 (d) to (g) are the Fourier transform spectra of different regions in (c); Figure 3As shown in (c) to (g), in the high-resolution transmission electron microscopy images, the Fourier transform spectra of the central region, branch region, interface region between the nanocrystal and the nanocrystal matrix, and the individual nanocrystal matrix region of the hexagonal nanocrystal show the same bright spots, and there is no rotation angle between them. This indicates that the nanocrystal and the nanosheet have a consistent single crystal structure. The nanocrystal is formed by orientational growth through the nanosheet matrix template, which further explains the reason for the orderly arrangement of the hexagonal nanoparticles.

[0055] Figure 4 This is a high-angle annular dark-field transmission electron microscopy (TEM) image of the nanosheets and hexagonal nanocrystals on the surface of the sample obtained in Example 1. Figure 4 Image (a) is an electron microscope image. Figure 4 (b) shows the element distribution of the boxed area in (a). Figure 4 (c) is a line scan elemental intensity diagram of the nanosheet surface particles in the dashed area of ​​(a). Figure 4 (d) represents the percentage of a specific component. From Figure 4 As shown in (b), the four elements Al, Fe, Cu, and O are uniformly distributed in the nanosheets and the particles on the nanosheet surface. The stronger brightness in the particle region is attributed to their accumulation along the thickness direction of the nanosheets. From Figure 4 As shown in (c) and (d), the intensity of each component in the nanosheets and nanoparticles exhibits consistent fluctuations, indicating that the nanosheets and nanoparticles have the same component proportions. The characterization result is Al. 14 Fe 24 Cu2O 60 The proportion of oxygen is also consistent with that of α-Fe2O3 rhombohedral crystal.

[0056] If the same preparation method as in Example 1 is used, the difference is that after washing the sample in step (5), it is freeze-dried at -40°C for 24 hours to obtain the product. Figure 5 The scanning electron microscope (SEM) image of the product shows that the nanosheet surface is clean and free of streaks, indicating that the formation of streaks is closely related to the liquid evaporation environment. Furthermore, the evaporation rate at the edges of the droplets is higher during evaporation, which facilitates preferential nucleation. Considering the structural and orientational consistency between the nanocrystals and nanosheets, it can be inferred that the formation of the strip-shaped hexagonal nanocrystals on the nanosheet surface is due to the coordinated effect of the droplet's stick-slip motion and the orientational growth of the edge nuclei.

[0057] The performance of the obtained product in the electrocatalytic reduction of nitrate to ammonia was evaluated, including the following steps: 5 mg of the product from Example 1 was taken as a catalyst sample and ultrasonically mixed with 50 μL of 5wt% Nafion solution and 950 μL of isopropanol for 1 hour to obtain a uniform black ink as a catalyst. Subsequently, 200 μL of the catalyst ink was uniformly coated onto a 1 cm² surface. 2 The working electrode is obtained by air-drying on nickel foam (NF) with a catalyst loading of 1 mg / cm³.2 Subsequently, the performance was evaluated in a three-electrode system using a CHI 660E electrochemical workstation. The catalyst-supported electrode was used as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as an Ag / AgCl electrode, and the electrolyte as a 1 mol / L KOH aqueous solution containing 0.1 mol / L KNO3.

[0058] The tests were conducted in an H-type electrolytic cell, with the anode and cathode chambers separated by a Nafion 211 membrane. The membrane pretreatment steps were as follows: first, soaking in a 50°C, 5wt% H₂O₂ aqueous solution for 1 hour; then, treatment in a 50°C, 0.1mol / L H₂SO₄ aqueous solution for 1 hour; finally, repeated rinsing with deionized water. All potentials were converted to the reversible hydrogen electrode (RHE) scale (E). RHE = E Ag / AgCl +0.059×pH + 0.197V), with a test potential range of -0.3V to -0.7V (vs. RHE).

[0059] Evaluation results as follows Figure 6 As shown, Figure 6 In the middle (a), Faraday efficiency is represented. Figure 6 (b) represents the yield. This indicates that the sample with hexagonal nanocrystals arranged in a striped pattern on the nanosheet surface exhibits excellent ammonia Faraday efficiency and yield, reaching its optimal value at a potential of -0.5V (relative to a reversible hydrogen electrode), with a Faraday efficiency of 91.23% and a yield of 13.42 mg h⁻¹. -1 cm -2 .

[0060] Example 2

[0061] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface, illustrating that the structural units of the stripes in this invention can achieve not only the hexagonal snowflake shape shown in Example 1, but also a spherical shape, comprising the following steps:

[0062] (1) Aluminum, copper and iron elements are mixed in an atomic ratio of 63:25:12 and uniformly melted in a vacuum induction melting furnace at a rated temperature of 1700℃ to obtain alloy ingots.

[0063] (2) The obtained alloy ingot is annealed in a furnace at 750°C for 2 hours.

[0064] (3) The annealed alloy ingot is crushed and screened to obtain 200-300 mesh powder particles.

[0065] (4) After preheating the powder in a 3 mol / L NaOH solution at 75°C for half an hour, place the powder in the solution and react at 75°C for 6 hours.

[0066] (5) After the reaction is complete, the sample obtained from the reaction is washed 8 times with deionized water to remove waste liquid. The reaction and washed sample are placed at room temperature for natural drying. A certain amount of water is reserved in the sample, and the solid-liquid ratio is 1.5 g / mL. After complete drying, the sample is characterized by scanning electron microscopy.

[0067] The main difference between Example 2 and Example 1 is the drying conditions in step (5). The drying conditions of the sample obtained from the reaction were changed from 90°C to room temperature natural drying.

[0068] Figure 7 These are scanning electron micrographs of the sample from Example 2. Figure 7 (a) shows the morphology of the nanosheets. Figure 7 Image (b) shows the stripe morphology on the nanosheet surface. It is evident that the stripe pattern on the nanosheet surface is shallower compared to the sample in Example 1. Figure 7 As can be seen from (b), this is mainly due to the fact that the structural units that make up the stripes have become spherical, and their particle size is smaller.

[0069] Figure 8 The image shows the particle size distribution of nanoparticles that form stripes on the surface of nanosheets, with a particle size of 18.8 ± 7.5 nm.

[0070] The working electrode for the sample in Example 2 was prepared using the same method as in Example 1, and the electrocatalytic reduction of nitrate to ammonia reaction was tested under the same experimental conditions. The results are as follows: Figure 9 As shown, Figure 9 In the middle (a), Faraday efficiency is represented. Figure 9 (b) shows the yield. This indicates that at a potential of -0.5V (relative to the reversible hydrogen electrode), the Faraday efficiency of the sample is only 76.35%, and the yield is 10.59 mg h. -1 cm -2 This performance is inferior to that of the striped array sample composed of hexagonal nanocrystals arranged in an orderly manner in Example 1.

[0071] The test results of Examples 1 and 2 confirm that nanosheets with ordered striped structural units on their surface exhibit higher catalytic efficiency for ammonia production. This may be due to the ordered orientation of the nanoparticles in Example 1, which leads to higher charge transfer efficiency during the catalytic process.

[0072] Example 3

[0073] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface, illustrating that the structural units of the stripes of the present invention can achieve not only the hexagonal snowflake shape in Example 1, but also a spherical shape, and the size of the spherical particles can be adjusted, including the following steps:

[0074] (1) Aluminum, copper and iron elements are mixed in an atomic ratio of 63:25:12 and uniformly melted in a vacuum induction melting furnace at a rated temperature of 1700℃ to obtain alloy ingots.

[0075] (2) The obtained alloy ingot is annealed in a furnace at 750°C for 2 hours.

[0076] (3) The annealed alloy ingot is crushed and screened to obtain 200-300 mesh powder particles.

[0077] (4) After preheating the powder in a 3 mol / L NaOH solution at 75°C for half an hour, place the powder in the solution and react at 75°C for 6 hours.

[0078] (5) After the reaction is complete, the sample obtained from the reaction is washed 8 times with deionized water to remove waste liquid. The reaction and washed sample is placed on a heating plate at 60°C for drying. A certain amount of water is reserved in the sample, and the solid-liquid ratio is 1.5 g / mL. After complete drying, the sample is characterized by scanning electron microscopy.

[0079] The main difference between Example 3 and Example 2 is that the drying temperature is adjusted to 60°C. Figure 10 This is a scanning electron microscope image of the sample prepared in Example 3. Figure 10 (a) shows the morphology of the nanosheets. Figure 10 Image (b) shows the stripe morphology on the surface of the nanosheets. (Compared to...) Figure 7 Similarly, the stripes on the surface of the nanosheets are also composed of spherical particles, but the colors of the stripes are more pronounced, thanks to the larger size of the spherical particles grown at 60°C. Figure 11 The particle size distribution of the spherical particles that form stripes on the surface of the nanosheets is statistically significant. The size of these particles is concentrated at 30.9 ± 8.6 nm, which is significantly larger than that of the spherical particles in Example 2.

[0080] Example 4

[0081] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface, illustrating that the morphology of the stripe building units of the present invention can not only achieve the hexagonal snowflake shape in Example 1, but also achieve spherical shapes and adjust the size of spherical particles, and can also prepare the stripe building units into concave nanoparticles of various shapes, including the following steps:

[0082] (1) Aluminum, copper and iron elements are mixed in an atomic ratio of 63:25:12 and uniformly melted in a vacuum induction melting furnace at a rated temperature of 1700℃ to obtain alloy ingots.

[0083] (2) The obtained alloy ingot is annealed in a furnace at 750°C for 2 hours.

[0084] (3) The annealed alloy ingot is crushed and screened to obtain 200-300 mesh powder particles.

[0085] (4) After preheating the powder in a 3 mol / L NaOH solution at 75°C for half an hour, place the powder in the solution and react at 75°C for 6 hours.

[0086] (5) After the reaction is complete, the sample obtained from the reaction is washed 8 times with deionized water to remove waste liquid. The reaction and washed sample is placed on a heating plate at 120°C for drying. A certain amount of water is reserved in the sample, and the solid-liquid ratio is 1.5 g / mL. After complete drying, the sample is characterized by scanning electron microscopy.

[0087] The main difference between Example 4 and Example 3 is that the drying temperature is adjusted to 120°C. Figure 12 This is a scanning electron microscope image of the sample obtained in Example 4. Figure 12 (a) shows the morphology of the nanosheets. Figure 12 (b) shows the morphology of the stripes on the surface of the nanosheets. It can be seen that the structural units of the stripes have been transformed into concave nanoparticles with different shapes and branches, and they are tightly connected. Figure 13 The particle size distribution of the concave nanoparticles is shown in the statistical diagram, with a size range of 61.1 ± 8.6 nm.

[0088] Comparative Example 1

[0089] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface, which differs from Example 1, involves absorbing residual water from the reaction powder before drying, so that the nanosheets of the final product do not form stripe patterns on their surface.

[0090] Specifically, steps (1) to (4) are the same as in Example 1.

[0091] Step (5) is as follows: After the reaction is completed, the sample obtained from the reaction is washed 8 times with deionized water to remove the waste liquid. Then, the residual water is removed with a dropper and absorbent paper. The sample is placed on a heating plate at 90°C to dry. After it is completely dried, it is characterized by scanning electron microscopy.

[0092] The main difference between Comparative Example 1 and Example 1 is that residual water was not retained during drying. Figure 14 This is a scanning electron microscope image of the sample obtained in Comparative Example 1. Figure 14 (a) shows the morphology of the nanosheets. Figure 14 (b) shows the surface morphology of the nanosheets. As can be seen, compared with Example 1, the nanosheets have transformed into a loose morphology, with dense star-shaped particles appearing on the surface. The particles are arranged in a more disordered manner and do not exhibit ordered stripe characteristics.

[0093] Comparative Example 2

[0094] A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface differs from Example 1 in that the concentration of NaOH involved in the reaction is adjusted to 1 mol / L, and the final product also fails to form ordered stripes.

[0095] Specifically, steps (1) to (3) and step (5) are the same as in Example 1.

[0096] Step (4) is as follows: After preheating the solution at 75°C for half an hour by placing it on a heating plate with 1 mol / L NaOH solution, the powder is placed into the solution and reacted at 75°C for 6 hours.

[0097] The sample was placed on a heating plate at 90°C to dry, and then characterized by scanning electron microscopy after it was completely dried.

[0098] The main difference between Comparative Example 2 and Example 1 is that the reaction concentration of NaOH was changed to 1 mol / L. Figure 15 This is a scanning electron microscope image of the sample obtained in Comparative Example 2. Figure 15 (a) shows the morphology of the nanosheets. Figure 15 In the middle (b), the surface morphology of the nanosheet is shown. It can be seen that the morphology of the nanosheet has changed, with a large number of hexagonal nanoparticles deposited on the surface, and no stripe features are observed.

[0099] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface, characterized in that, Includes the following steps: S1. Aluminum, copper and iron elements are weighed according to atomic ratio and placed in a vacuum induction melting furnace for uniform melting to obtain alloy ingots; S2. Anneal the alloy ingot obtained in step S1 in a furnace; S3. After crushing the annealed alloy ingot obtained in step S2, the ingot is sieved to obtain alloy powder. S4. After preheating the NaOH solution, the alloy powder obtained in S3 is placed into the solution to react, and the reaction is heated simultaneously. S5. After the reaction is complete, the product obtained in S4 is washed and then dried while retaining some moisture to obtain aluminum copper iron oxide nanosheets with ordered stripes on the surface. In step S5, during drying, the solid-liquid ratio of the product is 1.5 g / mL, and the drying temperature ranges from room temperature to 120°C. The nanosheets and the stripe patterns on their surfaces are all composed of single-crystal structures with an Al composition. 14 Fe 24 Cu2O 60 The crystal structure is α-Fe₂O₃ rhombohedral type, space group [missing information]. (167), JCPDS No. 33-0664.

2. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 1, characterized in that, In step S1, the purity of aluminum, copper and iron elements is 99.99%, and aluminum, copper and iron are mixed in an atomic ratio of 63:25:

12.

3. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 1, characterized in that, In step S1, the melting temperature is 1700℃.

4. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 1, characterized in that, In step S2, the annealing temperature is 750℃ and the annealing time is 2 hours.

5. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 1, characterized in that, In step S3, the target size for sieving the crushed alloy ingot is 200-300 mesh.

6. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 1, characterized in that, In step S4, the concentration of the NaOH solution is 2-4 mol / L, the preheating temperature and reaction temperature are 75℃, and the reaction time is 5-7 hours.

7. The method for preparing aluminum-copper-iron oxide nanosheets with ordered stripes on the surface according to claim 6, characterized in that, In step S4, the concentration of the NaOH solution is 3 mol / L.

8. The aluminum-copper-iron oxide nanosheets with ordered striations on the surface prepared by the method according to any one of claims 1 to 7, characterized in that, The stripe size on the surface of the nanosheet is in the nanometer range, and the stripe spacing is in the range of 80-130 nm.

9. The nanosheet according to claim 8, characterized in that, The surface stripe pattern of the nanosheet is composed of spherical, hexagonal snowflake-like, or irregularly concave nanoparticles.

10. The application of the nanosheets according to claim 8 or 9, characterized in that, When used in the electrocatalytic reduction of nitrate to ammonia, it achieved a maximum Faraday efficiency of 91.23% and a maximum yield of 13.42 mg / h at a voltage of -0.5 V relative to the reversible hydrogen electrode. -1 cm -2 .

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