Products and methods for thick-walled capped gold nanotubes

Abstract

This disclosure relates to a method (300) for producing thick-walled capped Au nanotubes (100). The method (300) includes: a. step (310) forming a first solution comprising a metal nanowire (110) and a first solvent, wherein the metal nanowire (110) is a nanowire of a first metal comprising silver and / or copper; b. step (320) adding a first Au complex to the first solution, thereby inducing galvanic substitution of the first metal with gold and / or chemical reduction of the first Au complex, to coat the metal nanowire (110) with gold and form an Au nanotube (120) around the metal nanowire (110); and c. step (360) adding a second Au complex and a growth inducer to the first solution, thereby growing gold on the Au nanotube (120) to form a thick-walled capped Au nanotube (100). After step c(360), the growth of gold on the Au nanotube is maintained for at least 1 minute. In step a and / or step b, a dispersing agent is added to the first solution. In steps a, b and / or c, a reducing agent is added to the first solution.

Description

[Technical Field]

[0001] This disclosure relates to the manufacture of nanotubes, gold nanotubes, and sacrificial template methods. [Background technology]

[0002] Metal nanowires, such as Ag nanowires, are widely used as high-aspect-ratio nanostructures in permeable electrodes and stretchable conductors, but they are not chemically stable. Au nanowires offer a biocompatible alternative that can provide high conductivity and stretchability, but to date, no high-aspect-ratio Au nanostructures exist that can be synthesized in large quantities using robust methods. Previous permeable electrodes and stretchable composites used Ag nanowires coated with a layer of Au. When exposed to corrosive conditions or mechanical wear, such Au-coated Ag nanowires can degrade and release silver, which can cause undesirable reactions. To date, no Au equivalent to Ag nanowires exists that is widely available and utilized.

[0003] There is a need to improve the provision of high aspect ratio nanostructures that offer long-term stability without corrosion, discoloration, or oxidation. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Currently, the simple production of large quantities of nanowires suitable for electronic applications is only possible with metals that are sensitive to the environment and readily degrade by oxidation, corrosion, UV light, and discoloration, such as silver and copper. The present invention relates to using nanowires of the said metal as sacrificial templates for producing more degradation-resistant metal nanotubes having properties suitable for electronic applications, wherein the sacrificial templates are removed from and / or embedded in the final Au nanotubes.

[0005] This invention relates to the novel synthesis of high aspect ratio Au nanotubes having a smooth surface structure and a narrow size distribution of nanotube diameters. The process uses metal nanowires, such as silver or copper, as templates. During the first and second gold coating steps, most of the metal nanowire template is removed. The final nanotubes show that they contain 99% wt% Au and exhibit stability under corrosive conditions. The process allows for selective control of the Au nanotube diameter by varying the initial Au nanotube concentration, as well as the Au complex and dispersant concentrations in the second coating step. The initial Au complex concentration limits the amount of Au that can be deposited on the Au nanotubes. The dispersant concentration affects both the thickness and uniformity of the Au coating, as well as the distribution of Au nanotube diameters after synthesis. Polyvinylpyrrolidone (PVP) has been used as a dispersant at concentrations of 1 wt% to 25 wt%, with the best coating uniformity and narrow diameter distribution obtained at 5 wt% or more of PVP. Furthermore, temperature (T) affects the second gold coating process, with growth much faster at T ≥ 60°C than at room temperature. The effect of pH can also depend on the gold complex and reducing agent used. In the case of ascorbate as a reducing agent, pH > 7 was used with good results. During the second growth process, pH in the range of 2–9 provided satisfactory results.

[0006] One object of the present invention is to provide stable gold nanotubes having capped ends. Since gold nanotubes have a hollow core, the ends of the tubes may be open so that the hollow interior of the tube is in contact with the surrounding medium, or they may be closed by a gold cap, thereby sealing the ends of the tubes. The latter situation is referred to here as “capped ends” or capped nanotubes. Capped nanotubes have several advantages, for example, they prevent the leakage of undesirable substances from the hollow core that may originate from processing or growth template residues. It should be recognized that such purity aspects are very important in biomedical applications and also very important for maintaining long-term stability in applications where trace amounts of chemical species can induce performance degradation, such as at highly sensitive interfaces in optoelectronic devices such as light-emitting diodes or solar cells. The cap can also define the accessible surface area of ​​the tube, and tubes with open ends have a large partially accessible internal area, which may contribute to the less distinct electrochemical response of the tube. The caps can further stabilize the nanotube structure and prevent the degradation into nanoparticles that was observed in thin-walled gold nanotubes without caps. [Means for solving the problem]

[0007] This was achieved, according to the present disclosure, using a method for producing thick-walled capped Au nanotubes. This method 300 is a. A step of forming a first solution comprising a metal nanowire and a first solvent, wherein the metal nanowire is a nanowire of a first metal comprising silver and / or copper, b. A step of adding a first Au complex to a first solution, thereby inducing galvanic displacement of the first metal by gold and / or chemical reduction of the first Au complex, to coat the metal nanowire with gold and form Au nanotubes around the metal nanowire, c. A step of adding a second Au complex and a growth inducer to the first solution, thereby growing gold on Au nanotubes to form thick-walled capped Au nanotubes. Includes.

[0008] After step c, the growth of gold on the Au nanotubes is maintained for at least 1 minute.

[0009] In step a and / or step b, a dispersant is added to the first solution.

[0010] In steps a, b, and / or c, a reducing agent is added to the first solution.

[0011] This has the advantage of providing a robust synthesis method for Au nanotubes with potential for expansion. Furthermore, it offers the advantages of highly conductive and stable Au nanotubes for applications requiring a combination of electrical conductivity, mechanical flexibility, large surface area, stability, corrosion resistance, and optical transparency.

[0012] In some embodiments, the method includes, after step b, adding a first metal etchant to the first solution to remove any remaining first metal.

[0013] This has the advantage of allowing the growth of gold after step c by removing at least some of the metal from the nanowires from the Au nanotubes formed around the metal nanowires grown after step b.

[0014] In some embodiments, the method includes, after step b, adding a first complexing agent configured to bond to the first metal, thereby inducing the dissolution of any salt of the first metal.

[0015] This has the advantage of allowing the growth of gold after step c to be carried out without the metal salt in the first solution.

[0016] In some embodiments, the method includes a step of performing dialysis, sedimentation and solvent exchange, and / or centrifugal solvent exchange after step b, thereby purifying the Au nanotubes. This also has the advantage of removing said metal and / or metal salt introduced into the solution by, for example, etching and / or dissolving any metal of the nanowire and the corresponding metal salt after step b.

[0017] This has the advantage of removing the old solution and seeds from step b from the first solution, enabling the growth of gold after step c, and thus enabling the first solution conditions for the second growth of gold after step c, which are substantially independent of the first solution conditions after step b.

[0018] In some embodiments, the method includes a step of adding a second complexing agent configured to bind to the first metal after step c, thereby inducing the dissolution of any salt of the first metal.

[0019] This has the advantage of enabling the removal of any metal salt deposited on the thick-capped Au nanotubes.

[0020] In some embodiments, the method includes a step of performing dialysis, sedimentation and solvent exchange, and / or centrifugal solvent exchange after step c, thereby purifying the thick-capped Au nanotubes.

[0021] This has the advantage of enabling the removal of any unwanted species in the first solution in the final thick-capped Au nanotube product. This also has the advantage of removing said metal and / or metal salt introduced into the solution by, for example, etching and / or dissolving any remaining metal of the nanowire and the corresponding metal salt after step c.

[0022] The disclosure further relates to a thick-walled capped Au nanotube that can be obtained by a process according to the method of claim 1, wherein the nanotube has an outer diameter-to-inner diameter ratio of at least 1.5, and the ends of the nanotube are capped with Au.

[0023] This disclosure further relates to thick-walled capped Au nanotubes. The Au nanotubes have an outer diameter difference of at least 10 nm between their outer and inner diameters. The nanotubes have an outer diameter-to-inner diameter ratio of at least 1.5. The ends of the nanotubes are capped with Au. The gold content of the nanotubes is at least 80 wt%.

[0024] This has the advantage of providing Au nanotubes with a high aspect ratio structure in which the optical properties vary depending on the inner and outer diameters of the nanotube. This further enables the production of thick-walled Au nanotubes, which improves stability compared to conventional thin-walled Au nanotubes that tend to decompose into nanoparticles over time. This further enables the production of thick-walled Au nanotubes with capped ends that prevent absorption of the surrounding medium during processing, thus enabling control of the purity of the product. This further enables the production of thick-walled Au nanotubes with capped ends that suppress leakage of metal residue from the core, thereby maintaining a chemically stable and inert surface of the Au nanotube.

[0025] In some embodiments, the thick-walled, capped Au nanotubes have a pentagonal prism shape. This can be advantageous because the surface of the pentagonal prism may be more energetically stable. Another advantage may be that the electrical contact between the Au nanotubes is improved by the pentagonal prism shape.

[0026] A solution comprising thick-walled capped Au nanotubes, a dispersant, and a solvent.

[0027] Au nanotube composite material, wherein the composite material comprises a polymer and the thick-walled capped Au nanotubes, and the composite material comprises an electrically conductive network of the thick-walled capped Au nanotubes.

[0028] This has the advantage of enabling electrical conductivity for the entire network, including Au nanotubes and polymer Au nanotube films. Furthermore, it allows the conductivity of the Au nanotube film to be tuned by tube density, tube geometry, and post-treatment of the tubes, such as thermal or optical sintering. The combination of polymer and an electrically conductive network of thick-walled, capped Au nanotubes provides mechanical robustness to the Au nanotube film, thereby providing a flexible or stretchable Au nanotube composite. When the binder in the composite is an elastomer, a stretchable conductor based on an Au nanotube-elastomer composite is formed. This further enables the formation of Au nanotube-PDMS composites that may have high conductivity and low Young's modulus, and their use has been demonstrated in in-vivo experiments.

[0029] This further offers the advantage of providing Au nanotube-polymer composites, such as nanotube-elastomer composites, which combine high electrical conductivity with mechanical flexibility, a Young's modulus of less than 10 MPa, non-toxicity, and chemical stability, making them excellent materials for biomedical applications. Since both Au and silicone elastomers are chemically stable over the long term and suitable for contact with biological tissues, Au nanotube-silicone elastomer composites containing silicone elastomers are particularly suitable for biomedical applications.

[0030] A permeable Au nanotube electrode, wherein the electrode comprises a substrate and the thick-walled capped Au nanotube, and the electrode comprises an electrically conductive network of the thick-walled capped Au nanotube disposed on the substrate.

[0031] In some embodiments, the electrically conductive network is partially embedded in a binder configured to fix the electrically conductive network to the substrate, and the electrically conductive network is at least partially accessible from the environment.

[0032] This has the advantage of providing electrodes that combine electrical conductivity and optical transparency. The sheet resistance of the transparent electrode decreases with increasing Au nanotube density, and the optical transparency also decreases with increasing Au nanotube density. High aspect ratio Au nanotubes can be beneficial for high-performance transparent electrodes with good transparency, such as over 90 wt%, and low sheet resistance, such as less than 10 ohms / square. This further enables the use of transparent conductive electrodes in a wide range of optoelectronic devices, such as displays, where light needs to pass through a conductive layer. Thick-walled, capped Au nanotubes can be combined with graphene, carbon nanotubes, and other transparent conductive materials such as conductive polymers, e.g., poly(3,4-ethylenedioxythiophene), PEDOT, etc., to form transparent conductive electrodes containing several conductive materials. Transparent conductive electrodes containing Au nanotubes can also be used in photoelectrochemical applications that combine light and electrical conductivity with electrochemistry. This further has the advantage of providing a high internal surface area for thick, at least 0.5 μm thick Au nanotube electrodes. High internal surface area is advantageous in electrochemical applications for charge storage and electrocatalysis. High-surface-area Au nanotube electrodes can form porous, self-supporting electrodes that allow liquid or gas flow through a film, which are of interest in electrocatalytic and sensing applications. [Brief explanation of the drawing]

[0033] [Figure 1a] This diagram shows a schematic process for growing thick-walled Au-capped nanotubes on metal nanowires. [Figure 1b] This diagram shows a schematic process for growing thick-walled Au-capped nanotubes on metal nanowires. [Figure 1c]This diagram shows a schematic process for growing thick-walled Au-capped nanotubes on metal nanowires. [Figure 1d] This diagram shows a schematic process for growing thick-walled Au-capped nanotubes on metal nanowires. [Figure 2a] This diagram shows a schematic conductive network of Au nanotubes in a permeable electrode. [Figure 2b] This diagram shows a schematic conductive network of Au nanotubes in a permeable electrode. [Figure 2c] This diagram shows a schematic conductive network of Au nanotubes in a permeable electrode. [Figure 2d] This diagram shows a schematic conductive network of Au nanotubes in a permeable electrode. [Figure 3] This diagram illustrates a method for growing Au nanotubes from Ag nanowires. [Figure 4] This figure shows an SEM image of an Au nanotube. [Figure 5] This figure shows a SEM image of a broken Au nanotube, revealing its hollow interior. [Modes for carrying out the invention]

[0034] Throughout the diagram, the same reference number refers to the same part, concept, and / or element. Therefore, unless otherwise explicitly stated, what is explained regarding a reference number in one diagram applies equally to the same reference number in other diagrams.

[0035] Terms and expressions The term nanowire refers to nanostructures in the form of wires with diameters ranging from a few nanometers to several hundred nanometers.

[0036] The term nanotube refers to tubular structures on the nanometer scale, such as nanowires with hollow cores. Typically, nanotubes have a specific surface area of ​​several square meters per gram, thereby allowing for a significantly larger surface area for interaction compared to the flat surfaces of larger structures.

[0037] The term capped nanotube refers to a nanotube with a closed end. Typically, the material of the cap at the end of the nanotube is the same material as the nanotube itself. It should be understood that capped nanotubes may be capped before the tubular portion of the capped nanotube is fully grown. Typically, a method for producing capped nanotubes is understood to be a method for producing a considerable number of capped nanotubes, since a large number of nanotubes are produced at once. Therefore, it should be understood that a method for producing uncapped nanotubes may, theoretically, occasionally form capped nanotubes due to the inherent randomness in growing nanotubes.

[0038] The term "solution" refers to both the formed solution and the solution after addition. For example, the first solution is formed using Ag nanowires in water and is named the first solution even after the addition of the first Au complex. In this example, the mixture of the second Au complex and the reducing agent in the second solvent is named the second solution, and the solution formed by adding the second solution to the first solution is typically called the first solution.

[0039] The term "gold complex" refers to a coordination compound containing one or more gold atoms. For example, a gold complex may be a gold salt in a solvent or a corresponding form.

[0040] Typically, gold complexes can be reduced so that the gold they contain is deposited in a solid form.

[0041] The term "gold salt" refers to compounds containing gold ions.

[0042] The term "dispersant" refers to a substance that helps prevent particles from clumping together. For example, during the production of gold nanotubes, dispersants may be used to prevent gold nanotubes from clumping together.

[0043] The term "growth inducer" refers to a substance that helps control the shape and size of nanoparticles during their formation. For example, during gold nanotube production, growth inducers may be used to control the surface structure, shape, and size of gold nanotubes. It should be understood that some substances have the ability to function as both dispersants and growth inducers.

[0044] The term reducing agent refers to a substance that donates electrons to another substance during a chemical reaction. For example, during the production of gold nanotubes, a reducing agent may be used to reduce gold ions in a gold salt to form gold nanotubes.

[0045] The term galvanic substitution refers to a process in which one type of metal ion is reduced by the oxidation of another metal atom. For example, during gold nanotube manufacturing, galvanic substitution may be used to deposit gold onto template nanowires made of another metal, such as silver or copper, to form gold nanotubes.

[0046] The term "complexing agent" refers to a substance that forms a complex with a metal ion, thereby increasing the solubility of the metal ion. For example, when gold nanotubes are grown on silver nanowires, AgCl can be formed, and AgCl can be dissolved by a silver complexing agent, such as ammonia or sodium thiosulfate. For example, ethylenediaminetetraacetic acid can be used as a copper complexing agent.

[0047] Figures 1a-c schematically illustrate the process of producing thick-walled capped Au nanotubes 100 from nanowires 110 using, for example, a sacrificial template method based on galvanic replacement and / or chemical reduction of a gold complex. Figure 1a represents the starting material of nanowires 110, Figure 1c represents the produced thick-walled capped Au nanotubes 100, and Figure 1b represents the intermediate process in which the Au nanotubes 120 are formed around the nanowires 110. In Figure 1c, the cap 140 covers the hollow interior 150 of the capped Au nanotube.

[0048] Figure 1a shows an exemplary metal nanowire. The nanowire has a high aspect ratio. In some examples, the aspect ratio is at least 10, at least 100, or at least 1000. Typically, a large number of nanowires in solution are used to produce Au nanotubes.

[0049] Several types of nanowires are commercially available. In some cases, nanowires are fabricated in solution. For example, Ag nanowires can be fabricated by polyol synthesis, and Cu nanowires can be fabricated by hydrazine reduction.

[0050] Currently, the simple production of large quantities of nanowires suitable for electronic applications is only possible with metals that are sensitive to the environment and readily degrade by oxidation, corrosion, UV light, and discoloration, such as silver and copper. Therefore, nanowires of these metals may be suitable as sacrificial templates for producing nanotubes of more degradation-resistant metals.

[0051] It should be understood that the nanowires may be made of silver, copper, and / or other metals, or combinations of metals.

[0052] In some examples, the metal nanowire 110 is of a first metal, which includes silver and / or copper. In some of these examples, the first metal is silver. In some of these examples, the first metal is copper.

[0053] Hereafter, the metal nanowire 110 described in the examples is Ag nanowire 110. It should be understood that the examples described for Ag nanowire 110, for example, the chemicals used to etch silver, also relate to corresponding examples adapted for nanowire 110 of other metals or combinations thereof.

[0054] In some examples, the Ag nanowire 110 has a diameter in the range of 1 to 200 nm. In some of these examples, the Ag nanowire 110 has a diameter in the range of 2 to 100 nm, 5 to 50 nm, 10 to 30 nm, 15 to 25 nm, or 7 to 60 nm.

[0055] In some examples, the Ag nanowire 110 has a length in the range of 1 μm to 400 μm. In some of these examples, the Ag nanowire 110 has a length in the range of 2 μm to 200 μm, 5 μm to 100 μm, 7 to 50 μm, 10 to 30 μm, or 15 to 20 μm.

[0056] In some examples, the Ag nanowire 110 has a length of at least 1 μm.

[0057] In some examples, the Ag nanowire 110 has a pentagonal prism shape. That is, the length of the Ag nanowire 110 corresponds to the height of the pentagonal prism, and therefore at least some cross-sections of the Ag nanowire 110 correspond to a pentagon.

[0058] In some examples, the Ag nanowire 110 has a cross-section that is pentagonal, cylindrical, and / or an intermediate rounded pentagon.

[0059] In some examples, growing gold on Ag nanowires 110 shaped as pentagonal prisms can result in thick-walled capped Au nanotubes 100 having a contour corresponding to the pentagonal prism. In some of these examples, the thick-walled capped Au nanotubes 100 have a pentagonal prism contour.

[0060] In some examples, the Au nanotube cap 140 consists of at least 90 wt% Au, at least 95 wt%, or at least 99 wt% Au.

[0061] In some cases, the thickness of the Au nanotube cap 140 is greater than the internal radius of the nanotube. In some cases, the thickness of the Au nanotube cap 140 is greater than the internal diameter of the nanotube. In some cases, the thickness of the Au nanotube cap 140 is greater than twice the internal diameter of the nanotube. In some cases, the thickness of the Au nanotube cap 140 is greater than three times the internal diameter of the nanotube.

[0062] In some examples, the shape of the Au nanotube cap 140 is elongated, and the distance from the end of the cap to the hollow core inside the nanotube is greater than the outer diameter of the nanotube. In some of these examples, the distance is greater than half the outer diameter of the nanotube.

[0063] In some examples, the shape of the Au nanotube cap 140 is elongated such that the distance from the end of the cap to the hollow core inside the nanotube is greater than twice the outer diameter of the nanotube.

[0064] In some examples, the shape of the Au nanotube cap 140 is elongated such that the distance from the end of the cap to the hollow core inside the nanotube is greater than the inner diameter of the nanotube.

[0065] In some examples, the shape of the Au nanotube cap 140 is elongated such that the distance from the end of the cap to the hollow core inside the nanotube is greater than 10 nm, greater than 20 nm, greater than 30 nm, greater than 50 nm, or greater than 100 nm.

[0066] In some examples, thick-walled, capped Au nanotubes have thick walls and caps configured to prevent leakage of undesirable material from the internal hollow core. The contents of the internal hollow core may originate from processing or growth template residues.

[0067] In some cases, when nanotubes without capped ends are used, solvents or polymer precursors may be absorbed into the hollow core and later released; therefore, thick-walled capped Au nanotubes are configured to produce composite materials of capped Au nanotubes and polymer binders.

[0068] In some cases, thick-walled, capped Au nanotubes are configured to prevent leakage from the hollow core into the environment, making them suitable for use in biomedical applications.

[0069] In some cases, thick-walled, capped Au nanotubes are configured to prevent leakage from the hollow core, thus providing long-term stability when capped Au nanotubes are used as an interface with a highly sensitive active layer in, for example, light-emitting diodes or photocells. The release of undesirable chemical species or ions from inside the nanotube can degrade the active layer(s) in such applications.

[0070] In some cases, thick-walled capped Au nanotubes, including high-purity capped Au nanotubes, can reduce the leakage of other trace elements in high-sensitivity applications, including biomedical, light-emitting diodes, and photocells.

[0071] In some cases, thick-walled capped Au nanotubes, including high-purity capped Au nanotubes, can be used in applications where contact with human or non-human animal skin is anticipated. The inertness of gold prevents allergic reactions that may be problematic when using other less inert metals such as nickel or copper.

[0072] In some cases, thick-walled, capped Au nanotubes are configured to have improved structural stability compared to thin-walled or uncapped tubes, because they do not have thin, exposed surfaces that are prone to structural degradation over time. In contrast, uncapped, thin-walled gold nanotubes have been observed to decompose into nanoparticles.

[0073] In some cases, thick-walled, capped Au nanotubes possess a clearly defined surface area, which can be advantageous in electrochemical applications. Uncapped tubes offer slower access to their internal surface area, resulting in a less distinct electrochemical response compared to capped tubes, which only allow access to the outer surface.

[0074] In some cases, capped ends provide a smoother and more stable interface, so thick-walled capped Au nanotubes have capped ends that are advantageous over open ends when in contact with biological tissue or cells.

[0075] Figure 1b shows an exemplary thin-walled Au nanotube 120 formed around an Ag nanowire 110. In this example, gold is grown on the Ag nanowire 110 by reduction of a gold complex and galvanic substitution of silver with gold. The Ag nanowire 110 may be an Ag nanowire 110 as described in Figure 1a.

[0076] In some examples, the Au nanotube 120 formed around the Ag nanowire 110 has a relatively thin gold layer, and the combined Au nanotube 120 and Ag nanowire 110 contain at least 10 wt% silver. In some of these examples, the combined Au nanotube 120 and Ag nanowire 110 have a silver content of at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 40 wt%, or at least 50 wt%.

[0077] In some examples, the Au nanotubes 120 formed around the Ag nanowires 110 have an outer diameter-to-inner diameter difference of up to 50 nm. In some of these examples, the Au nanotubes 120 formed around the Ag nanowires 110 have an outer diameter-to-inner diameter difference of up to 40 nm, up to 30 nm, up to 20 nm, up to 15 nm, up to 10 nm, or up to 5 nm.

[0078] In some examples, the Au nanotube 120 formed around the Ag nanowire 110 has a difference of at least 5 nm between its outer diameter and inner diameter.

[0079] In some examples, the process from the Ag nanowire 110 to the Au nanotube 120 formed around the Ag nanowire 110 in Figure 1a relates to the execution of a first step of gold growth on the Ag nanowire 110. In some of these examples, the first step of gold growth utilizes galvanic substitution of silver with gold and / or chemical reduction of a first gold complex.

[0080] Although the thin-walled Au nanotube 120 illustrated in Figure 1b is depicted as having a solid tube wall, it should be understood that the fabricated thin-walled Au nanotubes are typically porous or mottled, and therefore, even if the ends are capped, the metal nanowire 110 is accessible to the environment.

[0081] Figure 1c shows an exemplary thick-walled capped Au nanotube 100 formed by the process of growing gold on the Au nanotube 120 in Figure 1b.

[0082] In some examples, the thick-walled capped Au nanotube 100 is formed by performing a second step of gold growth on the Au nanotube 120 formed around the Ag nanowire in Figure 1b. In some of these examples, the first step of gold growth utilizes the chemical reduction of the second gold complex. In preferred examples, the thick-walled capped Au nanotube 100 is formed by growing gold on the Au nanotube 120 under different conditions than those used to grow gold on the Ag nanowire 110 to form the Au nanotube 120, for example by performing solvent exchange and / or removing silver and silver salts.

[0083] As shown in Figures 1a-b, in the process of forming multiple thick-walled capped Au nanotubes from an Ag nanowire via multiple Au nanotubes formed around the Ag nanowire, it should be understood that a significant proportion of the Au nanotubes form caps 140 at the ends of the Au nanotubes 120. The thick-walled capped Au nanotubes 100 can encapsulate any remaining silver or silver salts within the Au nanotubes 120, or at least significantly reduce their access from the environment, thereby reducing degradation and / or unwanted chemical interactions.

[0084] The thick-walled capped Au nanotube 100 includes an Au nanotube 120, and caps 140 at each end of the Au nanotube 120.

[0085] The Au nanotubes 120 formed around the Ag nanowire 110 in Figure 1b show the unsealed ends of the Ag nanowire 110. When a method is performed to produce multiple such Au nanotubes 120 formed around the Ag nanowire 110, it should be understood that the resulting Au nanotubes may include some Au nanotubes having gold at least partially covering the ends of the Au nanotubes.

[0086] Figure 1c shows, for illustrative purposes, the contour of the opening 150 of a tube and / or Ag nanowire closed by a cap 140, the contour of the capped opening 150 indicating the thickness of the thick-walled capped Au nanotube relative to the diameter of the Ag nanowire. In this example, the diameter of the thick-walled capped Au nanotube 100 is approximately three times the diameter of the Ag nanowire 110.

[0087] It should be understood that the Au nanotube 120 of the thick-walled capped Au nanotube 100 may also be the Au nanotube 120 described in Figure 1b, with additional gold grown on top.

[0088] In some examples, a thick-walled capped Au nanotube 100 restricts access to any silver and / or silver salts from the Ag nanowires within the Au nanotube 120. In some of these examples, the thick-walled capped Au nanotube 100 encapsulates the silver and / or silver salts.

[0089] After growing gold to form multiple Au nanotubes 120 around Ag nanowires 110, or after growing gold to form multiple thick-walled capped Au nanotubes 100, the final product can be improved by removing silver and / or silver salts.

[0090] In some examples, Ag nanowires 110 are etched off using Ag etchants while growing thick-walled capped Au nanotubes. In some of these examples, the Ag etchants include concentrated nitric acid, iron(III) nitrate, KI / 12 / H2O, and / or NH4OH*:H2O2:H2O / methanol. In some examples using copper nanowires, the copper is etched off with ammonium persulfate.

[0091] In some examples, Au nanotubes 120 and / or Au nanotubes 100 with thick-walled caps formed around Ag nanowires 110 are exposed to a solution containing ammonia configured to dissolve the silver salt.

[0092] In some examples, the thick-walled capped Au nanotube 100 is at least 80 wt% gold. In some of these examples, the gold content of the thick-walled capped Au nanotube 100 is at least 90 wt%, at least 95 wt%, at least 99 wt%, at least 99.5 wt%, or at least 99.9 wt%.

[0093] It should be understood that the gold content of thick-walled, capped Au nanotubes 100 is also determined by including any residual metals or salts thereof from the nanowires.

[0094] In some examples, the thick-walled, capped Au nanotubes 100 have a cross-sectional profile that is pentagonal, cylindrical, and / or an intermediate rounded pentagon.

[0095] In some examples, the thick-walled capped Au nanotube 100 has an outer diameter of at least 30 nm. In some of these examples, the thick-walled capped Au nanotube 100 has an outer diameter of at least 40 nm, at least 50 nm, at least 60 nm, at least 80 nm, at least 100 nm, at least 120 nm, at least 150 nm, or at least 200 nm.

[0096] In some examples, the thick-walled capped Au nanotube 100 has an outer diameter of up to 1 μm. In some of these examples, the thick-walled capped Au nanotube 100 has an outer diameter of up to 500 nm, up to 300 nm, or up to 200 nm.

[0097] In some examples, the thick-walled capped Au nanotube 100 has an outer diameter difference of at least 10 nm between its outer and inner diameters. In some of these examples, the thick-walled capped Au nanotube 100 has an outer diameter difference of at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at least 60 nm, at least 80 nm, at least 100 nm, at least 150 nm, or at least 200 nm between its outer and inner diameters.

[0098] In some examples, the thick-walled capped Au nanotube 100 has an outer diameter:inner diameter ratio (OD / ID) of at least 1.5. In some of these examples, the thick-walled capped Au nanotube 100 has an OD / ID of at least 1.7, at least 2, at least 2.5, at least 3, at least 4, at least 5, or at least 6.

[0099] In some examples, the thick-walled capped Au nanotube 100 has a length in the range of 100 nm to 400 μm. In some of these examples, the Au nanotube 100 has a length in the range of 200 nm to 200 μm, 500 nm to 100 μm, 1 to 50 μm, 4 to 30 μm, or 10 to 20 μm.

[0100] In some examples, the thick-walled capped Au nanotube 100 has a length of at least 1 μm.

[0101] In some examples, the Au nanotubes 100 with thick caps have an aspect ratio of at least 50. In some of these examples, the Au nanotubes 100 with thick caps have an aspect ratio of at least 100, at least 200, at least 400, at least 800, at least 1500, or at least 3000.

[0102] The growth of Au nanotubes by galvanic replacement reaction follows one of the following reactions depending on the gold complex. Au 3+ + 3Ag → Au 0 + 3Ag + Au + + Ag → Au 0 + Ag +

[0103] For example, the growth of Au nanotubes in Ag nanowires based on a pure galvanic replacement reaction has a theoretical outer diameter: inner diameter ratio, OD / ID, based on the following approximate volume calculation. OD / ID = (1 + n) 0.5 Au + For n = 1: OD / ID = 1.4 Au 3+ For n = 1 / 3: OD / ID = 1.15

[0104] It should be understood that the inner diameter of the thick-walled Au nanotubes 100 corresponds to the diameter of the Ag nanowires 110. In some examples, the inner diameter of the thick-walled Au nanotubes 100 can be smaller than the diameter of the Ag nanowires 110 in at least some regions due to the growth of gold inside the Au nanotubes before the ends of the Au nanotubes are capped.

[0105] As shown in Figures 1a-c, the process from the initial nanowire to the final nanotube is typically carried out in a solution containing a large number of nanowires and / or nanotubes. To reduce the aggregation of the nanowires and / or nanotubes, the solution also contains several dispersants. For example, if multiple Ag nanowires 110 in the solution do not disperse and eventually aggregate, it can be very difficult to uniformly grow gold on the Ag nanowires 110 to form separate, thick-walled, capped Au nanotubes 100.

[0106] In some examples, thick-walled, capped Au nanotubes 100 were prepared using dispersants including polyvinylpyrrolidone, PVP, and / or hexadecyltrimethylammonium bromide, CTAB.

[0107] In some examples, the thick-walled capped Au nanotubes have an outer diameter-to-inner diameter difference of at least 10 nm, and / or, nanotube 100 has an outer diameter-to-inner diameter ratio of at least 1.5, and / or, the ends of nanotube 100 are capped with Au, and / or, the gold content of nanotube 100 is at least 80 wt%.

[0108] Multiple thick-walled, capped Au nanotubes may be used to form an interconnected electrically conductive network. Due to the thick, capped Au nanotubes, such a conductive network may have advantageously robust and non-degrading properties.

[0109] The thick-walled capped Au nanotube 100 in Figure 1c is further related to a solution containing the thick-walled capped Au nanotube, the solution comprising the thick-walled capped Au nanotube 100, a dispersant, and a solvent. The dispersant is configured to prevent the thick-walled capped Au nanotube 100 from agglomerating during storage.

[0110] In some examples, at least 80% of the Au nanotubes in the solution are capped. In some of these examples, at least 90%, at least 95%, or at least 97% of the Au nanotubes in the solution are capped. An exemplary solution containing thick-walled capped Au nanotubes in which 95% of the Au nanotubes in the solution are capped should be understood to relate to a solution having thick-walled capped Au nanotubes with 5% capping defects.

[0111] Figures 2a to 2d show a schematic electrical conductivity network of Au nanotubes in a permeable electrode. Figure 2a shows the conductive network 210 of Au nanotubes 200 as is. Figure 2b shows a planar substrate 220, on which the conductive network 210 of Au nanotubes 200 is arranged. Figure 2c shows the conductive network 210 of Au nanotubes 100 arranged in the inner plane of the permeable polymer 240. Figure 2d shows the conductive network 210 of Au nanotubes 200 distributed throughout the permeable polymer 240.

[0112] Figure 2a schematically illustrates the electrically conductive network 210 of the Au nanotube 100. In some examples, the conductive network 210 of the Au nanotube is permeable and / or flexible. Typically, the Au nanotube 100 needs to be sufficiently thick and free of accessible reactive residue so that it retains conductivity over time and after the conductive network 210 of the Au nanotube 100 has been repeatedly bent.

[0113] In some examples, the conductive network 210 of Au nanotubes 200 includes thick-walled capped Au nanotubes 200 following one of the examples described in relation to Figure 1c.

[0114] Films and composites based on an electrically conductive network 210 of thick-walled Au-capped nanotubes 200 can offer one or more improved properties: high electrical conductivity, mechanical flexibility, large surface area, environmental stability, and optical transparency. In some examples, the sheet resistance of the conductive network 210 of thick-walled Au-capped nanotubes 200 is up to 10 ohms / sq. The caps on the Au nanotubes reduce the absorption of solvents and chemicals during the manufacturing of films and composites compared to the corresponding open Au nanotubes, which may harbor seeds inside. Capped Au nanotubes formed around Ag nanowires, for example, can also reduce the leakage of any residual silver from the core.

[0115] In some cases, the electrically conductive network 210 has a concentration of at least 0.05 mg / cm³. 2 It has a weight per unit area. In some of these examples, the electrically conductive network 210 has a weight of at least 0.1 mg / cm². 2 at least 0.2 mg / cm³ 2 at least 0.4 mg / cm³ 2 at least 0.8 mg / cm³ 2 , or at least 1.5 mg / cm³ 2 It has a weight per unit area.

[0116] In some examples, the sheet resistance of the conductive network 210 of thick-walled Au-capped nanotubes 200 is up to 0.1 ohms / sq, up to 1 ohm / sq, or up to 100 ohms / sq.

[0117] In some examples, the sheet transmittance at 550 nm of the conductive network 210 of the thick-walled Au-capped nanotubes 200 is at least 50%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97%.

[0118] In a preferred embodiment, the electrically conductive network 210 of Au nanotubes 100 has a sheet geometry structure, which may be planar or non-planar. It should be understood that the sheet geometry structure relates to the macroscopic geometry structure of the conductive network 210.

[0119] Figure 2b schematically illustrates the substrate 220, on which an electrically conductive network 210 of Au nanotubes 200 is installed.

[0120] In some examples, the conductive network 210 is fixed to the substrate 220 with a binder. In some of these examples, at least a portion of the conductive network 210 fixed with the binder is accessible, for example, to electrically connect to external electronic equipment.

[0121] In some examples, the conductive network 210 of Au nanotubes is encapsulated by the encapsulation layer 230.

[0122] In some examples, the substrate 220, the binder, and / or the encapsulation layer 230 are transparent. In some of these examples, they are transparent in the visible spectrum.

[0123] In some examples, the substrate 220, the binder, and / or the encapsulation layer 230 are flexible.

[0124] In some examples, the substrate 220, the binder, and / or the encapsulation layer 230 are electrical insulators.

[0125] In some examples, the surface of the substrate 220 on which the conductive network 210 of Au nanotubes 200 is arranged is a planar surface.

[0126] In Figure 2b, the substrate having the encapsulation layer 230 is shown as having a conductive network 210 of Au nanotubes completely surrounded by the substrate 220 and the encapsulation layer 230. Typically, at least a portion of the conductive network 210 of Au nanotubes is connected to an external conductor and / or external electronic equipment.

[0127] In some examples, at least two distinct areas of the conductive network 210 of the Au nanotube 200 are accessible.

[0128] A permeable Au nanotube electrode, wherein the permeable electrode comprises a substrate 220 and a thick-walled capped Au nanotube 200 following the thick-walled capped Au nanotube 100 in Figure 1c, and the composite material comprises an electrically conductive network 210 of the thick-walled capped Au nanotube 200.

[0129] Figure 2b further relates to the substrate 220 and the electrode 250 including an electrically conductive network 210 of Au nanotubes 200, wherein the conductive network 210 of Au nanotubes 200 is disposed on or on the substrate 220.

[0130] In some examples, the electrode 250 is a transparent electrode, and both the substrate 220 and the conductive network 210 are transparent to at least a certain range of the electromagnetic spectrum.

[0131] In some examples, the sheet transmittance of electrode 250 at 550 nm is at least 50%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97%.

[0132] Figure 2c schematically illustrates a layer of electrically conductive Au nanotube network 210, at least partially inside the flexible and permeable polymer 240.

[0133] In some examples, the layers of the conductive network 210 of Au nanotubes are planar layers.

[0134] In some examples, the sheet transmittance at 550 nm of the polymer containing the conductive network 210 is at least 50%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97%.

[0135] In some examples, polymer 240 includes an elastomer. In some of these examples, polymer 240 includes a silicone polymer and / or polydimethylsiloxane, PDMS.

[0136] In some cases, polymer 240 is an elastomer.

[0137] In Figure 2c, the electrically conductive network 210 of Au nanotubes is shown to be completely surrounded by the polymer 240. Typically, at least a portion of the conductive network 210 of Au nanotubes is connected to a conductor, such as a wire connected to an external electronic device.

[0138] In some examples, at least two distinct areas of the conductive network 210 of Au nanotubes are accessible.

[0139] Au nanotube composite material, wherein the composite material comprises a polymer 240 and thick-walled capped Au nanotubes 200 according to the thick-walled capped Au nanotubes 100 in Figure 1c, and the composite material comprises an electrically conductive network 210 of the thick-walled capped Au nanotubes 200.

[0140] Figure 2d schematically illustrates the electrically conductive network 210 of Au nanotubes 200 distributed throughout the flexible and permeable polymer 240.

[0141] In some examples, the sheet transmittance at 550 nm of the polymer 240 containing the conductive network 210 is at least 50%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97%.

[0142] In some examples, the polymer 240 and the conductive network 210 of Au nanotubes 200 form a composite material. In some examples, the composite material is in the form of a film, strip, and / or rod. In some of these examples, the film, strip, and / or rod has a thickness of up to 100 μm or a diameter of 100 μm.

[0143] In some examples, the conductive network 210 of polymer 240 and Au nanotubes 200 is mixed such that the Au nanotubes 200 are homogeneously distributed throughout the polymer 240.

[0144] In some examples, at least two distinct areas of the conductive network 210 of Au nanotubes are accessible.

[0145] Figure 3 illustrates a method for fabricating thick-walled capped Au nanotubes using metal nanowires, where the metal nanowires are Ag nanowires. This method 300 is... a. Step 310 to form a first solution containing Ag nanowires and a first solvent, b. Step 320, which involves adding a first Au complex to a first solution, thereby inducing galvanic substitution of silver by gold and / or chemical reduction of the first Au complex, to coat the Ag nanowires with gold and form Au nanotubes around the Ag nanowires. c. A second Au complex and growth inducer are added to the first solution, thereby growing gold on the Au nanotubes to form thick-walled, capped Au nanotubes (360) Includes, After step c360, the growth of gold on the Au nanotubes is maintained for at least 1 minute. In step a and / or step b, a dispersant is added to the first solution. In steps a, b, and / or c, a reducing agent is added to the first solution.

[0146] The method shown in Figure 3 is further related to corresponding methods using Cu nanowires, or nanowires containing silver and copper.

[0147] It should be understood that the dispersant typically needs to be present in the first solution at least after step b is completed to prevent the nanowires and / or nanotubes from agglomerating. The best method for introducing the dispersant may depend on the selection of the Ag nanowires and the first Au complex. For example, Ag nanowires may require a dispersant during the formation of the first solution.

[0148] In some examples, the dispersant is added during step 310 to form the first solution, and again in step c360. Typically, the dispersant is added to maintain a desired concentration of the dispersant when a considerable volume of liquid is added to the first solution.

[0149] It should be understood that the reducing agent typically needs to be present in the first solution at least after step c is completed in order to achieve sufficient gold growth. The best method for introducing the reducing agent may depend on the selection of Ag nanowires and the first Au complex. In one example, the addition of the first Au complex to the first solution in step b320 may result in sufficient galvanic substitution to coat the Ag nanowires with gold and form Au nanotubes. In another example, the addition of the first Au complex to the first solution in step b320 may necessitate the addition of a reducing agent to properly coat the Ag nanowires with gold and form Au nanotubes.

[0150] In some examples, step b induces galvanic substitution of silver with gold. In some of these examples, a reducing agent is added to the first solution in step a and / or step b to induce galvanic substitution of silver with gold and chemical reduction of the first Au complex. While it is possible to form Au nanotubes around the Ag nanowires shown in Figure 1b by galvanic substitution alone, it is typically preferable to utilize a reducing agent to improve and / or accelerate the growth of gold.

[0151] In a preferred embodiment of the method, step c includes adding a reducing agent to the first solution. Typically, it is desirable to add a reducing agent in step c because the opportunity for galvanic substitution may be lost during gold growth after step b.

[0152] After performing either step b or step c, gold growth occurs in nanowires and / or gold nanotubes. Typically, it is undesirable to wait for all available species to react, and the conditions in the first solution for desired growth may change as more gold grows; therefore, the growth process may be terminated by diluting the first solution or by lowering the temperature if the growth was performed at a high temperature.

[0153] In some examples, method 300 includes a first gold growth cessation step to terminate the gold growth induced by step b. In some examples, the first gold growth cessation step is performed for at least 5 minutes after step b. In some of these examples, the length of time between step b and the execution of the first gold growth cessation step is at least 10 minutes, at least 20 minutes, or at least 30 minutes.

[0154] In some examples, method 300 includes a second gold growth cessation step to terminate the gold growth induced by step c. In some examples, the second gold growth cessation step is performed for at least 5 minutes after step c. In some of these examples, the length of time between step c and the execution of the second gold growth cessation step is at least 10 minutes, at least 20 minutes, or at least 30 minutes.

[0155] In some examples, the second gold growth cessation step is performed when at least 80% of the grown Au nanotubes are capped. In some of these examples, the second gold growth cessation step is performed when at least 90%, at least 95%, or at least 97% of the grown Au nanotubes are capped. In some exemplary methods, it should be understood that the time to perform the second gold growth cessation step can be estimated based on empirical information in situations where it is not feasible to directly measure the percentage of capped Au nanotubes during gold growth.

[0156] In some examples, the first and / or second gold growth cessation step includes diluting the first solution to reduce or halt the growth of gold. In some of these examples, diluting the first solution includes adding to the first solution an amount of liquid equal to at least 50%, at least 100%, at least 200%, or at least 400% of the volume of the first solution.

[0157] In some examples, the first and / or second gold growth cessation step includes adding an oxidizing agent to react with the remaining reducing agent, thereby reducing or halting the gold growth. Examples of oxidizing agents are hydrogen peroxide and sodium hypochlorite.

[0158] In some examples, the first and / or second gold growth cessation step involves adding an acid and / or base to change the pH, thereby reducing or stopping the growth of gold. It should be understood that the first gold growth cessation step may be described as being included in step b, and the second gold growth cessation step may be included in step c. The first and second gold growth cessation steps were not described as being included in steps b and c in the examples in order to more clearly describe the examples that primarily explain the time between steps b / c and the first / second gold growth cessation steps.

[0159] In some examples, Ag nanowires have a pentagonal prism and / or cylindrical shape.

[0160] In some examples, the fabricated thick-walled capped Au nanotubes are thick-walled capped Au nanotubes as described by the example related to Figure 1c.

[0161] In some examples, the nanowire follows the nanowire 110 described by the example related to Figure 1a.

[0162] A thick-walled, capped Au nanotube as described by the example shown in Figure 1c.

[0163] In some examples, the first Au complex and / or the second Au complex contain at least one gold salt. It should be understood that the first Au complex and / or the second Au complex may each contain one or more Au complexes, and the first Au complex and / or the second Au complex may be different.

[0164] In some cases, the first Au complex and / or the second Au complex are Gold(III) chloride, HAuCl4, Gold(III) sulfate, Au2(SO4)3, Gold(III) nitrate, Au(NO3)3, Gold(III) perchlorate, Au(ClO4)3, Gold(III) trifluoroacetate, Au(CF3COO)3, Gold(III) acetate hydrate, Au(CH3COO)3, Gold(III) chloride trihydrate, AuCl3, Gold(III) nitrate, Au(NO3)3, Gold(III) sulfate, Au2(SO4)3, Gold(III) bromide, AuBr3, Gold(III) perchlorate, Au(ClO4)3, Gold(III) trifluoroacetate, Au(CF3COO)3, Gold(III) hydroxide, Au(OH)3, Gold(I) sodium sulfite, Na3Au(SO3)2, Gold(I) potassium sulfite, K3Au(SO3)2, Gold(I) ammonium sulfite, NH4Au(SO3)2, This includes sodium gold(I) thiosulfate, Na3[Au(S2O3)2], and / or any derivatives thereof, such as hydrates.

[0165] Hydroxide, OH - It should be understood that in solutions containing [unclear], some gold complexes may be replaced by hydroxides and thus altered from their original form. For example, gold chloride, in a high pH aqueous environment, all Cl - oh - It can be substituted with, and therefore may be gold hydroxide.

[0166] In some examples, the first solvent includes H2O, ethanol (EtOH), isopropyl alcohol (IPA), 1-propanol, dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), methanol, ethylene glycol, propylene glycol, and / or acetone isopropanol.

[0167] In some examples, a first solution containing a reducing agent is formed in step a310.

[0168] In some examples, the reducing agent includes lactic acid, folic acid, ascorbic acid, ascorbate, chitosan, hydroxylamine, hydroquinone, 2-pyrrolidone, sodium citrate, sodium borohydride, sodium metabisulfite, iron sulfate (ferrous sulfate), formaldehyde, hydrazine sulfate, and / or 2-pyrrolidone.

[0169] It should be understood that the reducing agents added in steps a, b, and / or c may be different reducing agents and / or combinations of reducing agents.

[0170] In some examples, step b320 includes adding a first Au complex and a reducing agent to the first solution. In some examples, the first Au complex comprises HAuCl4 tetrachloroaurate and the reducing agent comprises sodium citrate. In some examples, the first Au complex comprises HAuCl4 tetrachloroaurate and the reducing agent comprises ascorbate. In some examples, the first Au complex comprises HAuCl4 tetrachloroaurate and the reducing agent comprises hydroxylamine. In some examples, the first Au complex comprises gold(I) sulfite (Au(SO3)2). 3- It contains, and the reducing agent contains ascorbate. In some examples, the first Au complex is gold(I) sulfite Au(SO3)2 3- It contains, and the reducing agent contains hydroxylamine. In some examples, the first Au complex is gold(I) sulfite Au(SO3)2 3- It contains, and the reducing agent contains sodium citrate.

[0171] After step b320, the gold in the first Au complex may be replaced by silver, forming a layer of gold on the silver nanowires, although the growth of gold is typically improved by including a separate reducing agent configured to reduce the gold complex and form solid gold. Typically, once readily available silver is consumed / removed, a reducing agent is needed to maintain the growth of gold from the gold complex, for example, after the addition of the second Au complex in step c360.

[0172] In some examples, the first Au complex is configured to induce galvanic substitution between its gold and the silver of the Ag nanowire.

[0173] In some examples, the reducing agent includes Na2SO3 and ascorbate. In some of these examples, a first solution containing ascorbate is formed in step 310, and Na2SO3 is added in step b320. In some of these examples, a second solution is formed with Na2SO3 in the solvent and a first Au complex, and the second solution is added to the first solution.

[0174] It should be understood that it may be advantageous to keep one or more reducing agents separate from the Ag nanowires, the first Au complex, and / or each other before adding them all together in step b320.

[0175] In some situations, reducing agents, such as Na2SO3, can complex with certain Au complexes, reducing Au at least partially, thereby promoting further reduction and forming solid gold.

[0176] In some examples, step b320 includes forming a second solution comprising a first Au complex, and / or a reducing agent and a second solvent, and adding the second solution to the first solution. In some of these examples, the second solution comprises a dispersing agent.

[0177] It should be understood that the dispersant may be added to the first solution for the first time in step b320. Preferably, in order to keep the silver nanowires dispersed, the dispersant is already added in step a310 when the first solution is formed in 310. Typically, a certain type of dispersant is required for the successful growth of separate gold nanotubes.

[0178] In some examples, the dispersant includes polyvinylpyrrolidone, PVP, and / or glycine.

[0179] For example, when using polyvinylpyrrolidone as a dispersant, it may be preferable to use at least 5 wt% polyvinylpyrrolidone in the first solution.

[0180] In some examples, the solution after step b and / or step c contains at least 1 wt% of a dispersant. In some of these examples, the amount of dispersant is at least 2 wt%, at least 5 wt%, at least 7 wt%, or at least 10 wt%. The expression “after step b and / or step c” should be understood to refer to at least a portion of the gold growth period after the corresponding step.

[0181] In some examples, the growth of gold after step c360 is maintained for at least 1 minute. In some of these examples, the growth of gold after step c360 is maintained for at least 2 minutes, at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 60 minutes, or at least 120 minutes.

[0182] In some cases, the growth of gold after process c360 is maintained for up to 120 minutes.

[0183] In some examples, growing the gold after step c is carried out at least partially using a solution at a temperature of 30–100°C. In some examples, the solution temperature is at least 40°C, at least 50°C, at least 60°C, or at least 70°C.

[0184] In some examples, growing the gold after step b is carried out at least partially using a first solution in the pH range of 4–13. In some examples, the pH range is 5–12, 6–11, 7–10, and / or 8–9.

[0185] In some examples, growing the gold after step c is carried out at least partially using a solution within the pH range of 1 to 12. In some examples, the pH range is 1 to 4, 3 to 7, 4 to 10, 5 to 9, and / or 6 to 8.

[0186] In a preferred embodiment of the method, the growth of gold after step c is carried out using a solution with a pH of about 7 and using HAuCl4 as the second gold complex.

[0187] While solution pH affects gold growth in terms of both the rate and morphology of the growing gold, it should be understood that the ideal pH for desired growth depends on multiple factors such as the gold complex, reducing agent, solvent, and the metal of the nanowire. Furthermore, pH can also affect the function of the dispersant and other types of agents in the first solution, which in turn affects the agglomeration of Au nanotubes, the growth of gold, and the morphology taken by the metal of the nanowire.

[0188] In some examples, the growth inducer includes polyvinylpyrrolidone, 2-pyrrolidinone, N-methyl-2-pyrrolidone, hexadecyltrimethylammonium bromide, chloride ions, iron ions, L-arginine, and / or 1-ethyl-2-pyrrolidone.

[0189] In some cases, polyvinylpyrrolidone with molecular weights (Mw) ranging from 0.3 kDa to 3000 kDa is used as a growth inducer. In some of these cases, the molecular weight of polyvinylpyrrolidone is at least 3 kDa.

[0190] In some examples, at least one growth-inducing agent is added in step a and / or step b.

[0191] In some examples, method 300 includes step 330, after step b320, which involves adding an Ag etch to the first solution to remove any remaining Ag. In some of these examples, the first acid comprises ferric nitrate, ammonium hydroxide, and hydrogen peroxide.

[0192] It should be understood that numerous chemical substances are suitable for etching silver, and that many molecules can form complexes with silver.

[0193] In some examples, method 300 includes step 340, after step b320, to add a first silver complexing agent, thereby inducing the dissolution of any silver salt. In some of these examples, the first silver salt dissolving agent includes ammonia, cyanide, triphenylphosphine, thiosulfate, and thiocyanate. In some examples utilizing copper nanowires, ethylenediaminetetraacetic acid is used as the copper complexing agent. Typically, the dissolution of any silver or copper salt is carried out in aqueous solution. In some examples, step 340, in which the first silver complexing agent is added, includes replacing the solvent in the first solution.

[0194] Steps 330, which involve adding an Ag etch, and 340, which involve adding a first silver complexing agent, are related to removing accessible silver and silver salts from the Au nanotubes before adding the second Au complex, thereby enabling the utilization of chemicals and conditions that the silver or silver salts may have interfered with. In some examples, the Ag etch forms an Ag salt into which the first silver complexing agent dissolves.

[0195] In some examples, method 300 includes step 350, after step b320, dialysis, sedimentation and solvent exchange, and / or centrifugation solvent exchange, thereby cleaning the Au nanotubes.

[0196] In a preferred embodiment of the method, steps b320 and c360 are separated by step 350, which replaces most or all of the liquid in the first solution, thereby ensuring that the gold growth after step c360 is a separate gold growth and not a direct continuation of the gold growth after step b320. Between steps b320 and c360, step 330, which etches the metal of the nanowire, or step 340, which dissolves any salts of the nanowire, further separates the process of forming Au nanotubes around the nanowire and the process of forming thick-walled, capped Au nanotubes.

[0197] By replacing the solvent in the first solution before adding the second Au complex, it becomes possible to utilize the chemicals and conditions that the non-nanotube components of the first solution may have interfered with. It should be understood that the addition of an additional dispersant may be necessary to avoid nanotube aggregation after or during the solvent exchange.

[0198] In some examples, the reducing agent includes 2-pyrrolidone. In some examples, the reducing agent added in step c360 includes 2-pyrrolidone.

[0199] In some examples, the reducing agent includes commercially available PVP containing polyvinylpyrrolidone and 2-pyrrolidone residue, and therefore acts as both a dispersant and a reducing agent.

[0200] In some examples, method 300 includes step 370, after step c360, to add a second silver complexing agent, thereby inducing the dissolution of any silver salt in thick-walled capped Au nanotubes. In some of these examples, the second silver salt dissolving agent includes ammonia, cyanide, triphenylphosphine, thiosulfate, and thiocyanate. Typically, the dissolution of any silver or copper salt is carried out in aqueous solution. In some examples, step 370, in which the second silver complexing agent is added, includes replacing the solvent in the first solution.

[0201] In some examples, method 300 includes step 380 of performing dialysis, sedimentation and solvent exchange, and / or centrifugation solvent exchange after step c360, thereby cleaning the capped Au nanotubes.

[0202] It should be understood that the thick-walled, capped Au nanotubes themselves may be fully formed before step 380, which involves dialysis, sedimentation and solvent exchange, and / or centrifugation solvent exchange. However, the thick-walled, capped Au nanotubes are typically not considered a product until they are cleaned and / or extracted from the solution in which they were grown.

[0203] In some examples, the method includes the step of adding Ag etch to the first solution after step c360, thereby removing any remaining Ag. In some of these examples, the first acid includes ferric nitrate, ammonium hydroxide, and hydrogen peroxide.

[0204] It should be understood that the step of etching the metal of the nanowires and / or the step of dissolving the metal salt 370 after step c may make undesirable species soluble, and that the subsequent step of solvent replacement 380 allows the undesirable species to be removed from the first solution and the Au nanotubes.

[0205] The present invention further relates to thick-walled capped Au nanotubes that can be obtained by a process following one of the examples of methods described with respect to Figure 3. In some examples, the obtained thick-walled capped Au nanotubes have an outer diameter-to-inner diameter difference of at least 10 nm, and / or an outer diameter-to-inner diameter ratio of at least 1.5, and / or a gold content of at least 80 wt%.

[0206] In some examples, the process produces thick-walled, capped Au nanotubes, with at least 80% of the grown Au nanotubes being capped. In some of these examples, at least 90%, at least 95%, or at least 97% of the grown Au nanotubes are capped.

[0207] The thick-walled capped Au nanotubes that can be obtained by the process may be thick-walled capped Au nanotubes as illustrated by the example related to Figure 1c.

[0208] Figure 4 shows an SEM image of an Au nanotube exhibiting a thick-walled capped Au nanotube with a smooth surface and capped ends. The rounded ends and smooth surface indicate a nanotube structure that can protect the environment from any residual metal from the nanowire template. The thick-walled capped Au nanotube in the image has a diameter of approximately 100 nm and therefore provides a significantly more robust Au nanotube compared to the Au nanotube formed around the Ag nanowire shown in Figure 1b.

[0209] Figure 5 shows an SEM image of an Au nanotube, showing a thick-walled capped Au nanotube that has broken after being fabricated, revealing its hollow core. The approximate inner and outer diameters of at least some of the thick-walled capped Au nanotubes in the image appear to be about 20 μm and 100 μm, respectively, corresponding to the OD / ID of 5.

[0210] Exemplary manufacturing process for producing Au nanotubes, characterization of the Au nanotubes, integration of the Au nanotubes as an electrically conductive network in a device, and characterization of the electrically conductive network.

[0211] Preparation of Au complex precursors - HAuCl 468ul was diluted with 4.173ml of DI water. - Add 606 µl of NaOH (1M in water) at room temperature, then - The solution was stirred in a water bath at 60°C for 15 minutes in the dark. The solution took on a slightly yellowish-green color. - Cool the solution for 5 minutes while running cold tap water over it. - Carefully add 2.911 ml of Na2SO3 (0.1M in water), - Store the solution in the dark for 24 hours. The Au complex precursor will be observed as colorless.

[0212] Au coating of Ag nanowire templates - Disperse commercially available Ag nanowires (0.793 ml of a 5 mg / ml solution, 12 μm in length, 20 nm in width) in 4.996 ml of DI water and 5.271 ml of polyvinylpyrrolidone, PVP solution (molecular weight 55 k, 25 wt% in DI water) under stirring. - A glycine buffer solution is prepared by adding 2.5 ml of glycine solution (0.2 M in DI water), 0.386 ml of NaOH (1 M in DI water), and 7.114 ml of DI water. - Add 600 µl of glycine buffer, 194 µl of Na2SO3 (0.1 M DI in water), and 388 µl of Na ascorbate (1 M DI in water) to the Ag nanowire solution. - The Au complex precursor is added to the stirred Ag nanowire solution and stirred in the dark for 20 minutes to coat the Ag nanowires. - Dilute the Au-coated Ag nanowire solution with 7 ml of DI water per 1 ml of nanowire solution, and allow it to settle in the dark for one week. - Redisperse the solute in 6 ml of DI water and 0.4 ml of PVP (molecular weight 55k, 25 wt% in DI water) per 1 ml of the original solvent that was replaced.

[0213] Growth of thick-walled gold nanotubes - For the Au solution, dilute 4.24 µl of HAuCl4 (30 wt%) in dilute HCl in 3.875 ml of DI water. - Add 2.5 ml of Au-coated Ag nanowire solution to 2.636 ml of PVP (molecular weight 55k, DI 25 wt% in water), - Heat in a water bath at 60°C for 5 minutes. - Au solution is added to the heated nanowire solution, which is then called Au nanotube solution. - Heat in a water bath for 4 hours under continuous stirring. Here, the commercially available PVP in DI water contains 2-pyrrolidone residue so that the PVP and 2-pyrrolidone residue can function as reducing agents, dispersing agents, and growth inducers during the growth of thick-walled capped Au nanotubes.

[0214] Au nanotube purification - To dissolve the AgCl particles, add 45 µl of NH3 solution (0.5 M DI in water) per 1 ml of Au nanotube solution while stirring. - To replace the solvent, add 18 ml of Au nanotube solution and 10 ml of DI water to the vortex tube. - Centrifuge the Au nanotube solution at 1750 rpm for 5 minutes to allow the Au nanotubes to settle, and replace 15 ml of the solvent with 15 ml of DI water. - The nanotubes are redispersed by vortexing. This is repeated once. - For the third settling, the Au nanotube solution was centrifuged at 1500 rpm for 5 minutes, and 15.9 ml of solvent was replaced with 5 ml of DI water to dissolve the Au nanotubes in the same volume as immediately after the reaction before the purification step. - Maintain the Au nanotube solution at room temperature in the dark.

[0215] Au nanotube property evaluation Au nanotube morphology was imaged using SEM (Sigma 500, Zeiss) and TEM (FEI Titan3 60-300). For diameter analysis, nanowires were filtered on a PVDF film and washed with DI water. SEM images were taken from two different areas of each sample, and the diameters of four nanotubes in each image were measured, with the mean and standard deviation calculated. Elemental analysis using inductively coupled plasma sector-field mass spectrometry (ICO-SFMS) was outsourced. UV-vis absorption was measured using an Absorption Spectrometer Lambda 900 (PerkinElmer).

[0216] H2O2 corrosion test Solutions containing 0.1335 mg of nanotubes per 1 ml of solution (Au nanotube and Ag nanowire) were separately mixed with the same volume of hydrogen peroxide solution (5 wt%) and held at room temperature for 1 hour. Both solutions were analyzed by UV-vis absorption measurement (Absorption Spectrometer Lambda 900 PerkinElmer) and compared to the same nanotube / nanowire solutions dispersed in the same volume of DI water. The nanowire hydrogen peroxide solution was filtered over a PVDF membrane, washed with DI water, and imaged using SEM (Sigma 500, Zeiss) to observe morphological changes.

[0217] Fabrication of test devices Stretchable Au nanotube composite electrodes for electromechanical testing were fabricated as previously described for Au-TiO2 nanotubes (Lienemann et al., 2021) (Tybrandt et al., 2018). Using wax patterned vacuum filtration (Tybrandt and Voros 2016), contact pads (22 mm per device) were attached to each end on a poly(vinylidene difluoride) filter membrane. 2Au nanotube tracks (20 mm long, 0.5 mm wide) with a total area (see figure) were patterned. Depending on the nanowire density, 0.75 ml, 1.5 ml, or 3 ml of Au nanotube solution per device (4 to 8 devices on one filter) were used for filtration to produce tracks with thicknesses of approximately 1.5 μm, 3 μm, and 5 μm. The Au nanotube structures were transferred to polydimethylsiloxane (PDMS) Sylgard 184 (Dow Corning, 10:1) or Dragon Skin (DS) 10 Slow (Smooth-On, 1:1). First, an 80 μm thick lower layer of Sylgard was spin-coated onto a 2-inch silanated (trichloro(1H,1H,2H,2H-perfluorooctyl)silane) glass wafer at 1800 rpm for 30 seconds (3000 rpm for DS). The elastomer was partially cured on a hot plate at 70°C for approximately 9 minutes (approximately 10 minutes at room temperature for DS) until the material solidified but maintained its adhesive properties. Patterned Au nanotubes on the filter membrane were placed on the partially cured PDMS without applying any force, and then further cured on a hot plate at 70°C for 8 minutes while applying a weight of 500g. The Au nanotubes were transferred to the elastomer by wetting the filter membrane with DI water and peeling it off, leaving the nanowire structure. To penetrate the nanowire network, an intermediate layer of heptane:Sylgard solution (weight ratio 20:1, the same for DS) was spin-coated at 6000 rpm for 60 seconds and cured at 70°C for 5 minutes (approximately 3 minutes for DS). For the encapsulation layer, an additional 80 μm of Sylgard was spin-coated at 1800 rpm for 30 seconds (3000 rpm for 30 seconds in the case of DS) for the electromechanical test structure, while covering the contact area with foil (poly(ethylene naphthalate), Teonex, 25 μm thick). The foil was removed immediately after spin-coating, and the Sylgard sample was fully cured at 70°C overnight (70°C for 2 hours in the case of DS sample). For pure Sylgard or DS samples without nanowires, the lower layer was spin-coated as described above and similarly cured before adding encapsulation with the same parameters.

[0218] Electromechanical property evaluation Linear strain experiments to measure resistance used a motor-driven stage (X-LSQ300AE01, Zaber) and simultaneous resistance measurement with a Keithley 2701 digital millimeter. A 20 mm long and 0.5 mm wide sample was pulled at a speed of 0.2 mm / second until breakage, followed by 500 cycles each to 20%, 50%, and 100% strain at 2 mm / second. Stress-strain measurements were performed using a motor-driven linear stage (X-LSQ300A-E01, Zaber) and a force gauge (Mark-10 M5-2). Both samples with and without nanowires were cut into dumbbell shapes corresponding to the ISO 37-4 shape for tensile testing, reduced to two-thirds of their original size (to accommodate the very large maximum strain of DS samples within the limits of the linear stage) using a UV pulsed laser (MetaQuip Laser engraver FMHUV3W). The sample was mounted to a length of 12 mm and periodically pulled linearly at a rate of 0.12 mm / second between clamps until fracture occurred. For the Sylgard sample, the strain was increased by 20%, 50%, 100%, and 150% in each cycle, and for the DS sample, it was increased by 20%, 50%, 100%, 150%, 300%, and 600%.

[0219] Characterization of nanowire networks To evaluate crack formation during strain cycling, samples were imaged using a backlit optical microscope. After 500 cycles at 20%, 50%, and 100% strain, the samples were fixed at maximum strain for imaging.

[0220] In the example process described above, an extremely long AgNW (30 nm in diameter, 150 μm in length) was transformed into an Au nanotube with a diameter of approximately 100 nm and a length of 150 μm. The Au nanotube was then deposited on filter paper (0.22 mg / cm³). 2 The electrodes were then transferred to a styrene-ethylene-butylene-styrene (SEBS) substrate, thereby obtaining a stretchable, permeable electrode with an initial sheet resistance of 0.14 ohms / square and a transmittance of 70% for the Au nanotube layer at 550 nm.

Claims

1. A method for producing thick-walled capped Au nanotubes, wherein method (300) a. A step (310) of forming a first solution comprising a metal nanowire (110) and a first solvent, wherein the metal nanowire (110) is a nanowire of a first metal comprising silver and / or copper, b. A step (320) of adding a first Au complex to a first solution, thereby inducing galvanic substitution of the first metal by gold and / or chemical reduction of the first Au complex, to coat the metal nanowire (110) with gold and form an Au nanotube (120) around the metal nanowire (110), c. A step (360) in which a second Au complex and a growth inducer are added to the first solution, thereby growing gold in the Au nanotubes (120) to form thick-walled capped Au nanotubes (100) and Includes, After step c(360), the growth of gold on the Au nanotube is maintained for at least 1 minute. In step a and / or step b, a dispersant is added to the first solution. In steps a, b and / or c, a reducing agent is added to the first solution. method.

2. The method according to claim 1, wherein the growth inducer comprises polyvinylpyrrolidone, 2-pyrrolidinone, N-methyl-2-pyrrolidone, hexadecyltrimethylammonium bromide, chloride ions, iron ions, L-arginine, and / or 1-ethyl-2-pyrrolidone.

3. The method according to claim 1 or 2, wherein step c is performed in a solution within the pH range of 1 to 12.

4. The method according to any one of claims 1 to 3, wherein the growth of gold in step c is carried out at least partially using a solution at a temperature of 30 to 100°C.

5. The method according to any one of claims 1 to 4, further comprising the step (330) of adding a first metal etchant to the first solution after step b (320) to remove any remaining first metal.

6. The method according to any one of claims 1 to 5, further comprising step (340) of adding a first complexing agent configured to bond to a first metal after step b (320), thereby inducing the dissolution of any salt of the first metal.

7. The method according to any one of claims 1 to 6, further comprising, after step b (320), a step (350) of dialysis, sedimentation and solvent exchange, and / or centrifugation solvent exchange, thereby purifying the Au nanotubes.

8. The method according to any one of claims 1 to 7, further comprising step (370) of adding a second complexing agent configured to bond to the first metal after step c (360), thereby inducing the dissolution of any salt of the first metal.

9. The method according to any one of claims 1 to 8, further comprising step (380) of dialysis, sedimentation and solvent exchange, and / or centrifugation solvent exchange, thereby cleaning the thick-walled capped Au nanotubes after step c (360).

10. A thick-walled capped Au nanotube that can be obtained by a process according to the method of claim 1, wherein the nanotube (100) has an outer diameter-to-inner diameter ratio of at least 1.5, and the ends of the nanotube (100) are capped with Au.

11. A thick-walled capped Au nanotube, wherein the Au nanotube (100) has a difference of at least 10 nm between its outer diameter and inner diameter, the nanotube (100) has a ratio of at least 1.5 between its outer diameter and inner diameter, the ends of the nanotube (100) are capped with Au, and the gold content of the nanotube (100) is at least 80 wt%.

12. A solution comprising a thick-walled capped Au nanotube, the thick-walled capped Au nanotube (100) according to claim 11, a dispersant, and a solvent.

13. Au nanotube composite material, wherein the composite material comprises a polymer (240) and thick-walled capped Au nanotubes (100; 200) as described in claim 11, and the composite material comprises an electrically conductive network (210) of the thick-walled capped Au nanotubes (100; 200).

14. A permeable Au nanotube electrode, wherein the electrode (250) comprises a substrate (220) and thick-walled capped Au nanotubes (100; 200) as described in claim 11, and the electrode (250) comprises an electrically conductive network (210) of the thick-walled capped Au nanotubes (100; 200) disposed on the substrate (220).

15. A permeable Au nanotube electrode according to claim 14, wherein the electrically conductive network (210) is partially embedded in a binder configured to fix the electrically conductive network (210) to a substrate (200), and the electrically conductive network (210) is at least partially accessible from the environment.

Images