General synthetic strategy for fabricating multimetallic nanostructures

Abstract

A method for preparing hollow multimetal nanostructures, the method comprising the steps of: providing a first metal nanostructure having a plurality of first metal atoms, and performing a synthesis strategy comprising replacing a portion of the plurality of first metal atoms with a corresponding number of second metal ions, and promoting diffusion of the first metal atoms to provide the hollow multimetal nanostructure.

Description

[0001] This application is a divisional application of Chinese patent application No. 201911070563.7, filed on November 5, 2019, entitled "General Synthesis Strategy for Manufacturing Polymetallic Nanostructures". Technical Field

[0002] This disclosure relates to a method for preparing hollow multimetal nanostructures. Background Technology

[0003] Multimetallic hollow nanostructures are promising new candidates for applications in biomedicine, fuel cells, and gas sensors due to their porous structure and potential synergistic effects between two or more metals. However, known methods for synthesizing such nanostructures typically involve personalized synthetic approaches. While some general methods are known, these are generally limited to noble metals such as silver or palladium, both of which are expensive compared to other metals such as copper. Therefore, there is a need in the art for general synthetic strategies for preparing multimetallic nanostructures. Summary of the Invention

[0004] This disclosure relates throughout to a method for preparing hollow multimetallic two-dimensional nanostructures. The method may include providing a first metal nanostructure, replacing a portion of a first metal atom contained within the first metal nanostructure with a corresponding number of second metal ions, and promoting the diffusion of the first metal atoms to provide a hollow nanostructure. According to some aspects, the method may include a one-step synthesis strategy. This disclosure also relates to hollow multimetallic two-dimensional nanostructures provided by the method of the present invention. Attached Figure Description

[0005] Figure 1 An illustrative example of a method according to aspects of this disclosure is shown.

[0006] Figure 2 A scanning electron microscope (SEM) image of the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0007] Figure 3 Transmission electron microscopy (TEM) images of hollow Au-Cu two-dimensional nanostructures prepared according to Example II(a) are shown.

[0008] Figure 4 A high-resolution TEM (HRTEM) image of the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0009] Figure 5 High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0010] Figure 6 Energy-dispersive X-ray (EDX) imaging images of Cu elements in hollow Au-Cu two-dimensional nanostructures prepared according to Example II(a) are shown.

[0011] Figure 7 Energy-dispersive X-ray (EDX) imaging images of Au elements in hollow Au-Cu two-dimensional nanostructures prepared according to Example II(a) are shown.

[0012] Figure 8 The evolution of Cu-Au alloying over time is shown in Example II(a).

[0013] Figure 9A The X-ray photoelectron spectroscopy (XPS) of Au element in the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0014] Figure 9B The X-ray photoelectron spectroscopy (XPS) of Cu element in the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0015] Figure 10 The scattering spectrum of the hollow Au-Cu two-dimensional nanostructure prepared according to Example II(a) is shown.

[0016] Figure 11A SEM and TEM images of the Cu-Pd hollow nanostructure prepared according to Example II(b) are shown.

[0017] Figure 11B SEM and TEM images of the Cu-Pt hollow nanostructure prepared according to Example II(c) are shown.

[0018] Figure 11C SEM and TEM images of Cu-Au hollow nanotubes prepared according to Example II(d) are shown. Detailed Implementation

[0019] This disclosure relates throughout to a method for preparing hollow multimetallic nanostructures. The method may include providing a first metal nanostructure, replacing a portion of a first metal atom contained within the first metal nanostructure with a corresponding number of second metal ions, and promoting the diffusion of the first metal atoms to provide a hollow nanostructure. According to some aspects, the method may include a one-step synthesis strategy. This disclosure also relates to hollow multimetallic nanostructures provided by the method of the present invention. Optionally, the nanostructure may be two-dimensional.

[0020] As used herein, the term "nanostructure" refers to a structure having at least one dimension at the nanoscale, i.e., at least in dimensions between about 0.1 nm and 100 nm. It should be understood that "nanostructure" includes, but is not limited to, nanosheets, nanotubes, nanoparticles (e.g., polyhedral nanoparticles), nanospheres, nanowires, nanocubes, and combinations thereof. Nanosheets may include sheets having a nanometer-scale thickness. Nanotubes may include tubes having a nanometer-scale diameter. Nanoparticles may include particles in which each of their spatial dimensions is at the nanometer scale. Depending on some aspects, first metallic nanostructures and hollow multimetallic two-dimensional nanostructures may be the same or different.

[0021] According to some aspects, the method may include providing a first metallic nanostructure, such as a first metallic nanosheet. It should be understood that the first metallic nanostructure may be provided by any method known in the art and compatible with this disclosure.

[0022] For example, according to some aspects, the first metallic nanostructure may include copper nanosheets. According to some aspects, the copper nanosheets may be provided using a copper complex solution. According to some aspects, the copper complex solution may contain one or more copper complexes. As used herein, the term "copper complex" refers to a complex of copper with one or more complexing agents. Complexing agents useful according to this disclosure include, but are not limited to, tetradecylamine (TDA), dodecylamine (DDA), hexadecylamine (HAD), octadecylamine (ODA), and oleylamine (OLA). According to some aspects, the copper complex may be provided by mixing one or more copper atoms and / or their salts with one or more complexing agents in solution under an inert atmosphere and stirring at an acceptable temperature for an acceptable duration. For example, the copper complex may be provided by mixing a copper salt and one or more complexing agents in solution under a stream of inert gas. Examples of inert gases include, but are not limited to, nitrogen, argon, and combinations thereof. The mixed solution may then be heated to a temperature between about 100°C and 300°C for about one minute to about one hour to provide a copper complex solution containing the copper complex.

[0023] According to some aspects, copper nanosheets can be provided by heating a copper complex solution. For example, copper nanosheets can be provided by mixing a copper complex solution with one or more ligands at a high temperature under an inert atmosphere for an acceptable duration. For example, copper nanosheets can be provided by mixing a copper complex solution with ligands at a high temperature between about 100°C and 500°C, optionally between about 200°C and 400°C, and optionally about 300°C, under an inert atmosphere. The mixed solution can be held at the high temperature for a period of time between about one minute and two hours, optionally between about thirty minutes and ninety minutes, and optionally about one hour, thereby providing a copper nanosheet solution containing copper nanosheets. Examples of ligands include, but are not limited to, oleylamine, trioctylphosphine, tetradecylamine, dodecylamine, octadecylamine, hexadecylamine, trioctylphosphine oxide, oleic acid, and combinations thereof.

[0024] It should be understood that the first metal atoms contained in the first metal nanostructure (e.g., copper atoms contained in a copper nanosheet) will have a first oxidation potential. As used herein, the term "oxidation potential" refers to the energy change required to remove an electron from a material. It should be understood that, for example, copper may have an oxidation potential of about 0.34 V. According to some aspects, the first metal may be a metal having a first oxidation potential of no more than about 1.0 V, optionally no more than about 0.5 V. According to some aspects, the first metal may be selected from copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), and combinations thereof.

[0025] According to some aspects, the method may include replacing a portion of the first metal atoms contained in the first metal nanostructure with a corresponding number of second metal ions. According to some aspects, the second metal may include a metal having a second oxidation potential greater than the first oxidation potential. Examples of metals available according to this disclosure include, but are not limited to, gold (Au), platinum (Pt), palladium (Pd), and combinations thereof. According to some aspects, the second oxidation potential may be about 1.40 V (Au). 3+ / Au), approximately 1.20V (Pt) 2+ / Pt), and / or about 0.92V (Pd) 2+ / Pd). According to some aspects, the second oxidation potential may be at least about 0.6V greater than the first oxidation potential, optionally about 0.7V, optionally about 0.8V, optionally about 0.9V, and optionally about 1.0V. According to some aspects, the first metal is different from the second metal.

[0026] According to some aspects, replacing a portion of the first metal atoms contained in the first metal nanostructure with a corresponding number of second metal ions may include mixing a solution of the first metal nanostructure with a metal precursor solution. As used herein, the term "first metal nanostructure solution" refers to a solution containing the first metal nanostructure as described herein. As used herein, the term "metal precursor solution" refers to a solution containing a metal compound and / or its hydrate. Examples of metal compounds include, but are not limited to, chloroauric acid (HAuCl4), palladium(II) acetylacetonate (Pd(acac)2), chloroplatinic acid (H2PtCl6), combinations thereof, and their hydrates. According to some aspects, the first metal nanostructure solution may be mixed with the metal precursor solution at a temperature suitable for the second metal ions to replace a corresponding number of the first metal ions. For example, the first metal nanostructure solution may be mixed with the metal precursor solution at a high temperature between about 10°C and 200°C, optionally between about 50°C and 180°C, optionally between about 80°C and 180°C, and optionally between about 80°C and 150°C.

[0027] Depending on some aspects, the concentration and / or amount of the first metal nanostructure solution and / or metal precursor solution may be selected to provide a mixed solution having a first metal atom to second metal ion ratio of about 5:1 to about 1:5, optionally about 4:1 to 1:4, and optionally about 3:1 to 1:3.

[0028] According to several aspects, the molar ratio of the first metal atoms to the second metal ions can be selected to provide the selected composition and the resulting hollow multimetallic two-dimensional nanostructure phase. Specifically, according to several aspects, the reaction rate of electrodisplacement can increase with increasing metal precursor concentration. Therefore, the reaction rate of electrodisplacement can be selected by choosing a certain molar ratio of the first metal atoms to the second metal ions in the mixed solution.

[0029] The mixed first metal nanostructure and metal precursor solution can be maintained at high temperature for a synthesis time between about 1 minute and 3 hours, optionally between about 20 minutes and 2 hours, and optionally about 1 hour, such that a portion of the first metal atoms contained in the first metal nanostructure is replaced by a corresponding number of second metal ions. According to some aspects, the synthesis time can be selected to provide the selected composition and the resulting hollow multimetallic two-dimensional nanostructure phase. For example, a longer synthesis time (e.g., 20 minutes) can produce a hollow multimetallic two-dimensional nanostructure with a first metal atom to second metal atom molar ratio of about 1:1, while a shorter synthesis time (e.g., less than 5 minutes) can produce a hollow multimetallic two-dimensional nanostructure with a first metal atom to second metal atom molar ratio of about 3:1. Since the concentration of the first metal atoms contained in the nanostructure can decrease with increasing reaction time, when the reaction time is extended to 40 minutes, the first metal atom to second metal atom molar ratio can be reduced to 1:3. The final first metal atom to second metal atom molar ratio can reach 1:8, with a reaction time of 60 minutes.

[0030] According to some aspects, a portion of the replaced first metal ions may include first metal ions located at or near the surface of the first metal nanostructure. Without being bound by specific theory, because the first oxidation potential is less than the second oxidation potential, the first metal atoms at or near the surface of the nanostructure can be replaced by second metal ions due to electrochemical displacement.

[0031] According to some aspects, the method may include promoting the diffusion of first metal atoms to provide a hollow multimetallic two-dimensional nanostructure. Without being bound by a specific theory, the hollow multimetallic two-dimensional nanostructure may be provided by the Kirkendall effect, in which first metal atoms inside the first metal nanostructure diffuse to the outside of the nanostructure. As used herein, the term “outside” refers to a location at and / or near the surface of the nanostructure. The term “inside” refers to a location away from the surface of the nanostructure. It should be understood that the hollow multimetallic two-dimensional nanostructure may include, for example, continuous hollow centers (i.e., where hollow centers span from one side of the nanostructure to the other to form, for example, a ring-shaped or tubular nanostructure) and / or may include a hollow core (i.e., where hollow centers do not span from one side of the nanostructure to the other, but instead form concave centers or hollow centers in the nanostructure that are not visible from the outside of the nanostructure).

[0032] According to some aspects, one or more other method steps, as described herein, can sequentially and / or simultaneously promote the diffusion of the first metal atoms. For example, mixing a solution of the first metal nanostructure and a solution of the metal precursor at a high temperature suitable for the second metal ions to displace a corresponding number of the first metal ions and maintaining the mixture at the high temperature, as described herein, can sequentially and / or simultaneously displace a portion of the first metal atoms contained in the first metal nanostructure with a corresponding number of the second metal ions and promote the diffusion of the first metal atoms.

[0033] Depending on some aspects, the method may include a one-step synthesis strategy. As used herein, the term "one-step synthesis strategy" refers to a synthesis strategy in which at least a first reactant is converted into a reaction product in a single synthesis step. For example, as described herein, a first metal nanostructure can be transformed into a hollow multimetal two-dimensional nanostructure in a single synthesis step, specifically by mixing a solution of the first metal nanostructure and a solution of a metal precursor at a high temperature and maintaining the mixed solution at a high temperature for a certain period of time.

[0034] Figure 1 An illustrative example of a method according to aspects of this disclosure is shown. For example... Figure 1 As shown, the method may include providing one or more first metallic nanostructures, such as one or more copper nanosheets 11. The method may include replacing a portion of the copper atoms 12 contained in the copper nanosheets with a corresponding number of second metal ions such as Au ions 13, Pd ions 14, and / or Pt ions 15. As described herein, replacing a portion of the copper atoms 12 contained in the copper nanosheets with a corresponding number of second metal ions may include mixing a solution containing one or more copper nanosheets 11 with a metal precursor solution at a high temperature for a period of time. As described herein, carbon atoms may diffuse sequentially and / or simultaneously to provide a hollow multimetallic two-dimensional nanostructure 16 as described herein.

[0035] Depending on some aspects, the method may also include one or more washing steps. Washing steps may include centrifuging the solution containing the hollow multimetallic two-dimensional nanostructures, removing the supernatant, mixing with a solvent such as a hydrophobic solvent and / or an organic solvent, and centrifuging the mixed solution. The method may include one, two, three, or more washing steps.

[0036] It should be understood that, as used herein, the term "multimetallic" refers to at least two different metals. According to some aspects, a hollow multimetallic two-dimensional nanostructure can be a hollow bimetallic two-dimensional nanostructure, i.e., wherein the only metal atoms contained in the nanostructure are a first metal atom and a second metal atom. However, according to some aspects, a hollow multimetallic two-dimensional nanostructure can contain three, four, five, or more different kinds of metal atoms.

[0037] This disclosure also relates to hollow multimetallic two-dimensional nanostructures provided by the method of the present invention, including but not limited to Cu-Au hollow nanostructures, Cu-Pd hollow nanostructures, and Cu-Pt hollow nanostructures. According to some aspects, the molar ratio of the first metal atom to the second metal atom in the hollow multimetallic two-dimensional nanostructure can be about 10:1 to 1:10, optionally about 5:1 to 1:5, optionally about 3:1 to 1:3, optionally about 2:1 to 1:2, optionally about 1.5:1 to 1:1.5, and optionally about 1:1.

[0038] This disclosure also relates to methods using hollow polymetallic two-dimensional nanostructures as described herein. According to some aspects, the method may include utilizing hollow polymetallic two-dimensional nanostructures in the production of gas sensors and / or in the use of the resulting gas sensors. According to some aspects, the method may include using hollow polymetallic two-dimensional nanostructures to at least partially catalyze a CO2 reduction reaction.

[0039] While the aspects described herein have been described in conjunction with the foregoing exemplary aspects, various alternatives, modifications, variations, improvements, and / or substantially equivalents (whether known or currently unforeseen) will become apparent to at least those skilled in the art. Therefore, the exemplary aspects described above are intended to be illustrative and not restrictive. Various changes may be made without departing from the spirit and scope of this disclosure. Thus, this disclosure is intended to cover all known or subsequently developed alternatives, modifications, variations, improvements, and / or substantially equivalents.

[0040] Therefore, the claims are not intended to be limited to the aspects shown herein, but should be given the full scope consistent with the language of the claims, wherein, unless specifically indicated, references to elements in the singular are not intended to mean “one and only one,” but rather “one or more.” All structural and functional equivalents of the elements of the aspects known or hereafter known to those skilled in the art are expressly incorporated herein by reference and are intended to be covered by the claims. Furthermore, nothing disclosed herein is intended to be offered to the public, whether or not such disclosure is expressly shown in the claims. Unless an element is explicitly indicated by the phrase “for…”, no claim element should be construed as a manner plus function.

[0041] Furthermore, the word "example" used herein means "serving as an example, instance, or illustration." No aspect described herein as an "example" should necessarily be construed as preferred or advantageous over other aspects. Unless otherwise specifically stated, the term "some" means one or more. Combinations such as "at least one of A, B, or C," "at least one of A, B, and C," and "A, B, C, or any combination thereof" include any combination of A, B, and / or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as "at least one of A, B, or C," "at least one of A, B, and C," and "A, B, C, or any combination thereof" can be only A, only B, only C, A and B, A and C, B and C, or A and B and C, wherein any such combination may include one or more members of A, B, or C. Nothing disclosed herein is intended to be offered to the public, whether or not such disclosure is expressly shown in the claims.

[0042] As used herein, the terms “about” and “approximately” are defined as close to what is understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms “about” and “approximately” are defined as within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0043] Example

[0044] Example I: Preparation of copper complex solution

[0045] 100 mg of copper chloride (I) (99.99%), 220 mg of tetradecylamine (TDA, >96%), and 2 mL of ODE were added to a flask, where oxygen was removed under an Ar or N2 stream. After purging with Ar or N2 for 20 minutes, the mixture was heated to 190 °C on a hot plate and held at that temperature for 30 minutes. During heating, the TDA melted at approximately 38 °C to 40 °C and coordinated with Cu atoms to form a Cu-TDA blue complex solution.

[0046] Example II(a): Synthesis of Cu-Au hollow nanostructures

[0047] 6.0 mL of OLA (70%) was loaded into a 25 mL three-necked flask, where oxygen was removed by purging with Ar for 10 minutes. Under Ar flow, 0.5 mL of TOP (97%) and 0.5 mL of TOP (90%) were injected separately into the flask. After Ar flow for 10 minutes, the flask was rapidly heated to 300 °C. Next, 2 mL of the copper complex solution prepared in Example I was rapidly injected into the heated flask, and the reaction solution turned red within 5–10 minutes, indicating the formation of copper nanosheets. The reaction was maintained at 300 °C for 60 minutes. The reaction mixture was then allowed to cool naturally to 120 °C, and 1.0 mL of a gold precursor solution (0.1 M of 39.3 mg HAuCl4·3H2O dissolved in 1.0 mL of oleylamine) was injected. The reaction solution was maintained at 120 °C for 60 minutes. The product was separated by centrifugation at 8000 rpm for 5 minutes. The supernatant was discarded. A mixture of 5 mL hexane (or another hydrophobic solvent such as toluene or chloroform) and 5 mL ethanol was then added to the precipitate, and the mixture was centrifuged at 8000 rpm for 5 minutes. The washing procedure was repeated twice to remove unreacted precursors and surfactants. The Cu-Au hollow nanostructures were stored in hydrophobic solvents (e.g., hexane, toluene, and chloroform) prior to characterization.

[0048] The conclusion is that the injected gold precursor solution can be 0.2 mL to 3.0 mL, the injection temperature can be 80 °C to 150 °C, and the reaction time after injection can be 20 min to 120 min to provide acceptable results.

[0049] Example II(b): Synthesis of Cu-Pd hollow nanostructures

[0050] 6.0 mL of OLA (70%) was loaded into a 25 mL three-necked flask, where oxygen was removed by purging with Ar for 10 minutes. Under Ar flow, 0.5 mL of TOP (97%) and 0.5 mL of TOP (90%) were injected separately into the flask. After Ar flow for 10 minutes, the flask was rapidly heated to 300 °C. Next, 2 mL of the copper complex solution prepared in Example I was rapidly injected into the heated flask, and the reaction solution turned red within 5–10 minutes, indicating the formation of copper nanosheets. The reaction was maintained at 300 °C for 60 minutes. The reaction mixture was then allowed to cool naturally to 150 °C, and 1.0 mL of a gold precursor solution (0.1 M of 30.4 mg Pd(acac)2 dissolved in 1.0 mL of oleylamine) was injected. The reaction solution was maintained at 150 °C for 60 minutes. The product was separated by centrifugation at 8000 rpm for 5 minutes. The supernatant was discarded. A mixture of 5 mL hexane (or another hydrophobic solvent such as toluene or chloroform) and 5 mL ethanol was then added to the precipitate, and the mixture was centrifuged at 8000 rpm for 5 minutes. The washing procedure was repeated twice to remove unreacted precursors and surfactants. The Cu-Pd hollow nanostructures were stored in hydrophobic solvents (e.g., hexane, toluene, and chloroform) prior to characterization.

[0051] The conclusion is that the amount of palladium precursor solution injected can be 0.2 mL to 3.0 mL, the injection temperature of the palladium precursor solution can be 80 °C to 180 °C, and the reaction time after injection of the gold precursor solution can be 20 minutes to 120 minutes to provide acceptable results.

[0052] Example II(c): Synthesis of Cu-Pt hollow nanostructures

[0053] 6.0 mL of OLA (70%) was loaded into a 25 mL three-necked flask, where oxygen was removed by purging with Ar for 10 minutes. Under Ar flow, 0.5 mL of TOP (97%) and 0.5 mL of TOP (90%) were injected separately into the flask. After Ar flow for 10 minutes, the flask was rapidly heated to 300 °C. Next, 2 mL of the copper complex solution prepared in Example I was rapidly injected into the heated flask, and the reaction solution turned red within 5–10 minutes, indicating the formation of copper nanosheets. The reaction was maintained at 300 °C for 60 minutes. The reaction mixture was then allowed to cool naturally to 120 °C, and 1.0 mL of a platinum precursor solution (0.1 M of 51.7 mg H₂PtCl₆·6H₂O dissolved in 1.0 mL of oleylamine) was injected. The reaction solution was maintained at 120 °C for 60 minutes. The product was separated by centrifugation at 8000 rpm for 5 minutes. The supernatant was discarded. A mixture of 5 mL hexane (or another hydrophobic solvent such as toluene or chloroform) and 5 mL ethanol was then added to the precipitate, and the mixture was centrifuged at 8000 rpm for 5 minutes. The washing procedure was repeated twice to remove unreacted precursors and surfactants. The Cu-Pt hollow nanostructures were stored in hydrophobic solvents (e.g., hexane, toluene, and chloroform) prior to characterization.

[0054] The conclusion is that the amount of platinum precursor solution injected can be 0.2 mL to 3.0 mL, the injection temperature of the platinum precursor solution can be 80 °C to 150 °C, and the reaction time after injection of the platinum precursor solution can be 20 minutes to 120 minutes to provide acceptable results.

[0055] Example II(d): Synthesis of Cu-Au hollow nanostructures

[0056] 6.0 mL of OLA (70%) was loaded into a 25 mL three-necked flask, where oxygen was removed by purging with Ar for 10 min. Under Ar flow, 0.2 mL of TOP (97%) was injected into the flask. After Ar flow for 10 min, the flask was rapidly heated to 300 °C. Next, 2 mL of the copper complex solution prepared in Example I was rapidly injected into the heated flask, and the reaction solution turned red within 5–10 min, indicating the formation of copper nanosheets. The reaction was maintained at 300 °C for 20 min. The reaction mixture was then allowed to cool naturally to 120 °C, and 1.0 mL of a gold precursor solution (0.1 M of 50.7 mg HAuCl4·3H2O dissolved in 1.0 mL of oleylamine) was injected. The reaction solution was maintained at 120 °C for 60 min. The product was separated by centrifugation at 8000 rpm for 5 min. The supernatant was discarded. A mixture of 5 mL hexane (or another hydrophobic solvent such as toluene or chloroform) and 5 mL ethanol was then added to the precipitate, and the mixture was centrifuged at 8000 rpm for 5 minutes. The washing procedure was repeated twice to remove unreacted precursors and surfactants. The Cu-Au hollow nanostructures were stored in hydrophobic solvents (e.g., hexane, toluene, and chloroform) prior to characterization.

[0057] The conclusion is that the injected gold precursor solution can be 0.2 mL to 3.0 mL, the injection temperature can be 80 °C to 150 °C, and the reaction time after injection can be 20 min to 120 min to provide acceptable results.

[0058] Example III: Characterization of Hollow Nanostructures

[0059] The surface morphology of the hollow nanostructures obtained in Example II was investigated using a scanning electron microscope (SEM, QUANTA FEG 650) from FEI, with a field emitter as the electron source. Transmission electron microscopy (TEM) images were captured using a FEITecnai 20 microscope with an accelerating voltage of 200 kV. Energy dispersive X-ray spectroscopy (EDS) images and high-angle annular dark-field (HAADF) images were obtained using a Titan microscope with probe correction at an accelerating voltage of 300 kV. 3TMAcquisition was performed at 80-300 s / TEM. Extinction spectra of the hollow nanostructures were recorded using a UV-Vis-NIR spectrometer (Cary 5000). X-ray diffraction (XRD) patterns were obtained using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation, operating at a tube voltage of 40 kV and a current of 40 mA. The surface composition of the Cu nanosheets was determined using X-ray photoelectron spectroscopy (XPS, Kratos Axis). This instrument was equipped with a monochromatic (Al Kα) X-ray gun. The binding energy was calculated by calibrating the binding energy of the C1s peak to 284.6 eV.

[0060] Figure 2-7 The structure and composition characterization of the Cu-Au two-dimensional nanostructure prepared according to Example II(a) are shown.

[0061] Figure 2 The scanning electron microscope (SEM) images clearly show that the hollow Au-Cu two-dimensional nanostructures have an average diameter of 75 nm. Since the electrodisplacement reaction does not change the size of the Cu nanosheets, hollow Cu-Au two-dimensional nanostructures with similar size ranges can also be obtained based on the prepared Cu nanosheets, which range from 45 nm to several micrometers in size. The determination of the effect of the electrodisplacement reaction on the formation of hollowness is crucial. 3+ The potential of Au (1.40V) is higher than that of Cu. 2+ At the potential of Cu (0.34V), this reaction, 2Au 3+ +3Cu→2Au+3Cu 2+ This will happen automatically. Therefore, the substitution of Cu atoms leads to the formation of hollow nanostructures.

[0062] Figure 3 The transmission electron microscope (TEM) images shown and such Figure 5 The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements shown further confirm that the Cu-Au two-dimensional nanostructure has hollow pores.

[0063] Figure 4 The high-resolution TEM (HRTEM) image of the single hollow nanostructure shown reveals that it contains large crystalline regions. The stripes with a grid spacing of 2.225 Å indicate the (111) plane of the centered cubic (fcc) alloy Cu-Au nanostructure.

[0064] Figure 5 This image shows an energy-dispersive X-ray (EDX) image of a hollow nanostructure. Figure 6 and Figure 7 EDX images of Cu and Au are shown respectively. Figure 5-7As shown, Cu and Au are uniformly distributed throughout the hollow nanostructure. This indicates that the Cu-Au hollow nanostructure is in the alloy phase.

[0065] The transformation from the pure Cu fcc phase to the alloy Cu-Au phase was further confirmed by X-ray diffraction. Figure 8 The evolution of Cu-Au alloying over time in Example II(a) is shown. Specifically, Figure 8 The evolution of Cu-Au alloying is shown, exhibiting a decrease in Cu(111) diffraction peak intensity and an increase in Cu-Au(111) diffraction peak intensity.

[0066] Specifically, Figure 8 (a) This shows that the pure Cu phase was obtained after reacting with the Cu precursor at 300 °C for 60 minutes. The diffraction peak of Cu(111) is located at 43.7°, as shown in the image. Figure 8 As shown in (a).

[0067] After injecting the Au precursor into a Cu nanosheet solution at 120°C for 5 minutes, the reaction was continued. Figure 8 (b) indicates the formation of a mixed phase, as the diffraction peak of Cu-Au(111) appears at 40.8°. The porous structure also confirms the electrodisplacement reaction occurring on the Cu sheet surface, as shown in the inserted SEM image 81 and TEM image 82.

[0068] With the reaction time extended to 20 minutes Figure 8 (c) The diffraction peaks indicating Cu(111) decrease to almost negligible levels, suggesting that the product is now predominantly a Cu-Au alloy phase. Measurements showed that the Cu concentration decreased with increasing reaction time at the same Au precursor inoculation concentration. When the reaction time was less than 5 minutes, the Cu to Au molar ratio was approximately 3:1. When the reaction time was extended to 40 minutes, the Cu to Au molar ratio decreased to 1:3. After extending the reaction time to 60 minutes, the final Cu to Au molar ratio reached 1:8. Since the electrodisplacement reaction rate increased with Au precursor concentration, it was found that the Cu to Au molar ratio and the time required to form the hollow structure decreased with increasing Au precursor concentration. Therefore, the composition and phase of the Cu-Au two-dimensional nanostructure can be tuned by controlling the reaction time and inoculation concentration of the Au precursor.

[0069] The electronic properties and surface composition of the Cu-Au two-dimensional nanostructure were further examined using X-ray photoelectron spectroscopy (XPS). Figure 9A and Figure 9B The XPS spectra show well-resolution peaks from Au 4f and Cu 2p. Both Cu 2p peaks are positively shifted, i.e., Cu 2p... 1 / 2 It is 0.2 eV and Cu 2p5 / 2 The binding energy is 0.3 eV. The change in binding energy may be due to electron transfer from Cu to Au, and can also be explained by the difference in work function between Cu(111) (4.65 eV) and Au(111) (5.10 eV). Furthermore, both peaks of Au 4f are positively shifted, i.e., Au 4f and Au 4f , respectively. 7 / 2 It is 0.2 eV and Au 4f 5 / 2 The value was 0.13 eV. This change is attributed to Au losing electrons to surface ligands. XPS analysis showed that there were no separated Au or Cu phases in the two-dimensional nanostructure, which is consistent with the XRD results and EDX imaging images.

[0070] The phase transition from pure Cu to Cu-Au alloys can also be observed through a redshift in their scattering spectra. The absorption peak of pure Cu nanosheets is located at approximately 600 nm. After forming a two-dimensional hollow Cu-Au nanostructure, the extinction peak is redshifted to the infrared region (centered at 1500 nm), as shown below. Figure 10 As shown. This redshift can be attributed to a decrease in aspect ratio during electrical displacement or to changes in electronic structure due to phase transition. Two-dimensional hollow Cu-Au nanostructures with unique optical properties have potential applications in surface-enhanced Raman scattering (SERS), sensing, and biomedical fields.

[0071] Figure 11A and Figure 11B SEM 111 and TEM 112 images of Cu-Pd and Cu-Pt hollow nanostructures prepared according to Examples II(b) and II(c), respectively, are shown. Specifically, these SEM and TEM images demonstrate that, due to Pd... 2+ / Pd(0.92V) and Pt 2+ The high oxidation potential of / Pt (1.20V) allows for the formation of hollow Cu-Pd and Cu-Pt two-dimensional nanostructures. The sizes of these two types of hollow nanostructures can be controlled from 50 nm to a few micrometers.

[0072] Figure 11C SEM image 111 and TEM image 112 of Cu-Au nanotubes prepared according to Example II(d) are shown. Specifically, TEM image 111 indicates that the Cu-Au nanotubes have a rough surface and sharp ends, which can act as a highly efficient catalyst for reducing CO2 or as a gas sensor.

Claims

1. A ring-shaped nanostructure comprising a first metal atom and a second metal atom, The first metal atom includes copper. The second metal atom is selected from the group consisting of gold, platinum, palladium, and combinations thereof.

2. The ring-shaped nanostructure according to claim 1, wherein the first metal atom has a first oxidation potential and the second metal atom has a second oxidation potential, the second oxidation potential being at least 0.6V greater than the first oxidation potential.

3. The cyclic nanostructure according to claim 1, wherein the molar ratio of the first metal atom to the second metal atom is 10:1 to 1:

10.

4. The cyclic nanostructure according to claim 3, wherein the molar ratio is 2:1 to 1:

2.

5. The cyclic nanostructure according to claim 3, wherein the molar ratio is about 1:

1.

6. A ring-shaped nanostructure obtained by a method comprising: A first metal nanosheet having a first metal atom, wherein the first metal atom includes copper, and Execute a synthesis strategy, the synthesis strategy including: A portion of the first metal atoms is replaced by a corresponding number of second metal ions, and Promote the diffusion of the first metal atoms to provide the ring-shaped nanostructure.

7. The cyclic nanostructure according to claim 6, wherein the first metal atom has a first oxidation potential and the second metal ion has a second oxidation potential, the second oxidation potential being greater than the first oxidation potential.

8. The cyclic nanostructure according to claim 6, wherein the molar ratio of the first metal atom to the second metal ion is 10:1 to 1:

10.

9. The cyclic nanostructure according to claim 8, wherein the molar ratio is about 1:

1.

10. The cyclic nanostructure according to claim 6, wherein the second metal ion is selected from the group consisting of gold, platinum, palladium, and combinations thereof.

11. The cyclic nanostructure of claim 6, wherein the portion of replacing the first metal atom with the corresponding number of second metal ions comprises mixing a first metal nanosheet solution comprising a first metal nanosheet with a metal precursor solution comprising a metal precursor, the first metal nanosheet comprising the first metal atom and the metal precursor comprising the second metal ions.

12. The cyclic nanostructure according to claim 11, wherein the metal precursor is selected from the group consisting of chloroauric acid, palladium(II) acetylacetonate, chloroplatinic acid, combinations thereof, and their hydrates.

13. The cyclic nanostructure according to claim 11, wherein the first metal nanosheet solution is mixed with the metal precursor solution at a high temperature between 50°C and 180°C.

14. The cyclic nanostructure according to claim 13, wherein the mixed first metal nanosheet solution and the metal precursor solution are held at the high temperature for a synthesis time between 1 minute and 3 hours.

Images