Nanomaterials

Abstract

A method for preparing noble metal nanomaterials includes: (A) adding an aqueous solution of a noble metal ion source and a reducing agent to an aqueous solution of an organic compound to form a reaction mixture, wherein the organic compound is capable of 2D planar stacking in the aqueous solution; and (B) separating the noble metal nanomaterial from the reaction mixture. This application also relates to noble metal nanomaterials prepared according to this method.

Description

Technical Field

[0001] This invention relates to a method for preparing noble metal nanomaterials and the noble metal nanomaterials themselves. Background Technology

[0002] Two-dimensional (2D) nanomaterials, which are only a few atomic layers thick but have a larger lateral area, have sparked tremendous research interest. Graphene, for example, possesses unique electronic, mechanical, and surface-related properties due to its relatively low thickness but large area.

[0003] Freestanding ultrathin 2D metallic nanostructures have a wide range of potential applications. Compared to 3D materials, the increased exposure of active metal sites endows them with higher catalytic activity. Furthermore, the lower resistivity of 2D metallic nanostructures also suggests potential applications in batteries and electronic devices. 2D metallic nanostructures can also be used in surface plasmon resonance (SPR) technology. SPR is a fundamental principle in many technologies, including optical sensing, semiconductor optical absorption enhancement, and other color-based biosensor technologies. This technology has potential medical applications, including photothermal therapy for cancer treatment.

[0004] Currently, the methods for producing 2D metallic nanomaterials can be broadly classified into physical and chemical methods. Physical methods include compression under high temperature and high pressure conditions, as well as repeated size reduction through repeated folding or compression stacking of metal sheets. These methods can currently obtain metallic nanomaterials with a minimum thickness of 0.9 nm (S Yang et al., Mater. Chem. Front., 2, 2018, 456-467).

[0005] Chemical techniques typically involve the use of soluble metal precursors. Nanomaterial growth is initiated by using a reducing agent to ultimately reduce the soluble metal to neutral metal atoms. These atoms provide nucleation sites for the growth of the nanomaterials.

[0006] Many chemical techniques require the use of solid substrates, such as mica, silica, and graphite, on which metal films are grown. US-A-2008 / 166259 describes the use of immobilized micelles on a solid substrate surface as sites for the reduction of noble metals, including platinum and gold. This method can form metal nanoparticles with a thickness of 2 nm–5 nm. The thickness, shape, and size of the nanoparticles can be controlled by changing the surfactant.

[0007] Producing ultrathin 2D metallic nanomaterials without a solid substrate is a significant challenge. This is because metal atoms have a natural tendency to form highly isotropic 3D close-packed lattices. Introducing confinement materials can suppress this natural tendency, thereby inducing anisotropic growth, which is essential for the production of 2D metallic nanostructures. To date, a range of synthetic strategies have employed various confinement materials to prevent the free growth of primary metal nuclei and promote 2D anisotropic growth. These confinement materials include surfactants (e.g., polymers and reactive gases selectively bound to low-refractive-index metal surfaces) and templates (e.g., layered hydrogels, graphene, and graphene derivatives).

[0008] Ultrathin Rh nanosheets with a reported thickness of 0.4 nm have been successfully synthesized using poly(vinylpyrrolidone) polymer supports (Y. Li et al., Nat. Commun., 5, 2014, 3093). However, this method requires very high reaction temperatures.

[0009] Au nanosheets have also been prepared using a layered bilayer structure of itaconic acid dodecyl glycerol (DGI). By varying the concentration of DGI to influence the spacing between the bilayers in the layered structure, the thickness of the nanosheets can be adjusted from a few nanometers to tens of nanometers (J. Jin et al., J. Am. Chem. Soc., 135, 2013, 12544-12547). However, this method cannot produce metallic nanostructures with atomically thin layers. Summary of the Invention

[0010] This invention seeks to improve the formation of noble metal nanomaterials by providing wet chemical synthesis of freestanding (i.e., substrate-free) metal nanostructures (e.g., ultrathin nanosheets).

[0011] According to a first aspect, the present invention provides a method for preparing noble metal nanomaterials, comprising:

[0012] (A) An aqueous solution of a noble metal ion source and a reducing agent are added to an aqueous solution of an organic compound to form a reaction mixture, wherein the organic compound is capable of 2D planar stacking in the aqueous solution; and

[0013] (B) Separate the noble metal nanomaterial from the reaction mixture.

[0014] Typically, nanomaterials are characterized by the presence (preferably predominantly present) of nanostructures with an ultrathin dimension (e.g., their thickness). For example, 50% or more of the nanostructures may have an ultrathin dimension in terms of quantity size distribution.

[0015] Nanomaterials are characterized by the presence (preferably predominantly present) of nanostructures selected from nanosheets, nanofilms, nanoplates, nanosheets (e.g., nanosheets with atomic-level thickness) and their hierarchical superstructures (e.g., superstructures of nanosheets, such as quasi-spherical ones).

[0016] In a preferred embodiment, the nanomaterial is characterized by the presence (preferably predominantly) of nanosheets.

[0017] Nanosheets can have atomic-level thickness.

[0018] The thickness of the nanosheets, measured by atomic force microscopy (AFM), may not exceed 15 times the atomic radius of the noble metal (e.g., empirical measurements according to J.S. C. Later, J. Chem. Phys., 41, 1964, 3199-3205). Preferably, the thickness of the nanosheets, measured by atomic force microscopy (AFM), is not greater than 10 times the atomic radius of the noble metal (e.g., empirical measurements according to J.S. C. Later, J. Chem. Phys., 41, 1964, 3199-3205). Particularly preferably, the thickness of the nanosheets, measured by atomic force microscopy (AFM), is not greater than 6 times the atomic radius of the noble metal (e.g., empirical measurements according to J.S. C. Later, J. Chem. Phys., 41, 1964, 3199-3205).

[0019] The thickness of the nanosheets measured by atomic force microscopy (AFM) is no more than 8 atomic layers. Preferably, the thickness of the nanosheets measured by AFM is no more than 5 atomic layers. Particularly preferably, the thickness of the nanosheets measured by AFM is no more than 3 atomic layers.

[0020] The average thickness of the nanosheets can be 0.50 nm or less (measured by atomic force microscopy (AFM)). Preferably, the average thickness of the nanosheets is in the range of 0.40 nm to 0.50 nm.

[0021] The thickness distribution of the nanosheets (measured by atomic force microscopy (AFM)) can range from 0.26 nm to 0.54 nm.

[0022] In a preferred embodiment, the nanomaterial is characterized by the presence (preferably predominantly) of nanoplates (e.g., single-crystal nanoplates).

[0023] The average thickness of the nanoplate can be 5 nm or greater (measured by atomic force microscopy (AFM)).

[0024] The average side length of the nanoplate can be 100 nm or larger (measured by TEM).

[0025] Noble metal nanomaterials can be either elements or alloys.

[0026] Precious metals can be elements selected from gold (Au), silver (Ag), platinum (Pt), iridium (Ir), osmium (Os), ruthenium (Ru), palladium (Pd), and rhodium (Rh).

[0027] Preferably, the precious metal is Au or Pt. Particularly preferably, the precious metal is Au.

[0028] The noble metal ion source can be a noble metal compound. The noble metal compound can be an organometallic compound. The noble metal compound can be an acidic compound. The noble metal compound can be a noble metal halide. Preferably, the noble metal compound is a noble metal chloride (e.g., HAuCl4).

[0029] The reducing agent can be a citrate / ester (e.g., a salt or ester of citric acid). The reducing agent can be a Group I or Group II metal citrate.

[0030] Preferably, the molar ratio of the reducing agent to the noble metal ion source in the reaction mixture is less than 15. Particularly preferably, the molar ratio of the reducing agent to the noble metal ion source in the reaction mixture is in the range of 8 to 12.

[0031] Preferably, the molecules of the organic compound self-associate or self-assemble in an aqueous solution.

[0032] Preferably, the organic compound is capable of forming a plate-like stack in an aqueous solution.

[0033] Preferably, the organic compound is capable of providing intermolecular interactions in two orthogonal directions (e.g., along the x and y axes). These intermolecular interactions can be hydrophobic interactions in the xy plane and π-π interactions in the z direction.

[0034] Preferably, the organic compound has an affinity for noble metal ions. This affinity can be attributed to metal-π interactions and / or chelation.

[0035] Organic compounds can undergo hydrogen bonding.

[0036] The molecules of organic compounds may contain at least one heteroatom.

[0037] Preferably, the organic compound is an organic amphiphilic molecule.

[0038] In a preferred embodiment, the molecule of the organic compound comprises a rigid aromatic moiety, a hydrophilic moiety, and a hydrophobic moiety.

[0039] Preferably, the organic compound has the following molecular formula:

[0040]

[0041] in:

[0042] R is hydrogen or C. n H 2n+1 Partial, where 0 < n ≤ 6;

[0043] R' is C m H 2m+1 Partial, where 0 < m ≤ 6;

[0044] Z is a bond or a diazenyl or diazenylbenzene linkage; and

[0045] Y is a part containing a carboxyl group, a carbonyl group, a hydroxyl group, an acid anhydride, an amino group, an amide group, a thiol group, or a sulfonyl group.

[0046] Preferably, Y is a carboxyl-containing moiety or a sulfonyl-containing moiety. Particularly preferably, Y is SO3Na or CO2H.

[0047] Preferably, Z is a diazonyl or diazonylbenzene moiety.

[0048] Preferably, each of R and R' can be the same or different, and can be methyl or ethyl.

[0049] Preferably, the organic compound is selected from methyl orange, ethyl orange, p-methyl red, methyl red, sodium dichloroisocyanurate, 4-(dimethylamino)benzoic acid, 4-methylaminobenzoic acid and 2,2'-bipyridine.

[0050] Organic compounds can be azo or non-azo compounds.

[0051] Organic compounds can be azo compounds (e.g., dyes), such as methyl orange, ethyl orange, p-methyl red, methyl red, or sodium dichloroisocyanurate.

[0052] The organic compound can be a non-azo compound, such as 4-(dimethylamino)benzoic acid, 4-methylaminobenzoic acid, 2,2'-bipyridine, or a 2,2'-bipyridine derivative.

[0053] Preferably, in step (A), the aqueous solution of the noble metal ion source and the reducing agent are added sequentially to the aqueous solution of the organic compound.

[0054] The method may also include:

[0055] (A1) Let the reaction mixture stand for a period of time (e.g., about 12 hours).

[0056] Step (B) can be performed by centrifugation. The product of step (B) can be a precipitate. The product (e.g., precipitate) can be washed once or several times with ultrapure water until the supernatant is colorless.

[0057] Step (A) can be performed at ambient temperature (e.g., in the temperature range of 0°C to 50°C). Preferably, step (A) is performed in the temperature range of 10°C to 30°C.

[0058] At ambient temperature, the time for the reaction to reach completion is typically less than 24 hours (e.g., in the range of 10 to 14 hours).

[0059] Step (A) can be performed under environmental stress.

[0060] By changing the molar ratio of the organic compound to the noble metal ion source, the formation of different types of metal nanomaterials can be controlled. For example, at a low molar ratio, the nanomaterials may be characterized by the presence (preferably predominantly) of ultrathin metal nanosheets and nanoplatelets. At a high molar ratio, the nanomaterials may be characterized by the presence (preferably predominantly) of advanced nanostructures.

[0061] Preferably, the molar ratio of the organic compound to the noble metal ion source in the reaction mixture is 2 or less. Particularly preferably, the molar ratio of the organic compound to the noble metal ion source in the reaction mixture is in the range of 0.10 to 0.5.

[0062] In a preferred embodiment, the method further includes:

[0063] (A') Add an aqueous solution of the inorganic salt to the reaction mixture.

[0064] This implementation scheme allows for the advantageous formation of single-crystal metal nanoplates, the thickness of which and the side length can be controlled by changing the molar ratio of inorganic salt to noble metal ion source.

[0065] The inorganic salt can be a Group 1 metal salt or a transition metal salt. Preferably, the inorganic salt is an iron salt or a sodium salt.

[0066] The inorganic salt can be a halide. Preferably, the inorganic salt is a bromide.

[0067] Preferably, in step (A'), the molar ratio of the inorganic salt to the noble metal ion source in the reaction mixture is less than 1. Particularly preferably, the molar ratio of the inorganic salt to the noble metal ion source in the reaction mixture is in the range of 0.1 to 0.8.

[0068] According to another aspect, the present invention provides a noble metal nanomaterial as defined above.

[0069] The noble metal nanomaterial can preferably be obtained by the method defined above. Attached Figure Description

[0070] The present invention will now be described with reference to specific embodiments and the following accompanying drawings. These embodiments and drawings should not be considered as limiting the scope of the invention.

[0071] Figure 1 : Molecular structure applicable to the selection of organic compounds in this invention.

[0072] Figure 2 : Molecular structures suitable for further selection of organic compounds of the present invention.

[0073] Figure 3 Photographs and UV-Vis spectra of the reaction mixture according to Example 1 after 12 hours.

[0074] Figure 4 a and Figure 4 b: Bright-field TEM image of the ultrathin metal nanosheets according to Example 1.

[0075] Figure 4 c: Dark-field STEM image of the ultrathin metal nanosheets according to Example 1.

[0076] Figure 5 TEM images of 20 different ultrathin metal nanosheets from Example 1 and their calculated fractal dimension values.

[0077] Figure 6 AFM images of five ultrathin metal nanosheets from Example 1, with the thickness of three nanosheets along the marked white lines shown in the inset.

[0078] Figure 7 Histogram of average thickness data of 30 different ultrathin metal nanosheets according to Example 1, obtained by AFM.

[0079] Figure 8 a: HRTEM image of the ultrathin metal nanosheets according to Example 1.

[0080] Figure 8 b: The ultrathin metal nanosheets according to Example 1 <111> SAED map in the region axis.

[0081] Figure 8 c: XRD patterns of the ultrathin metal nanosheets according to Example 1 at 2θ in the range of 30° to 60°.

[0082] Figure 9 Representative TEM images of the ultrathin metal nanosheets from Example 1 at different points during the reaction.

[0083] Figure 10 The UV-Vis spectra of the reaction mixture from Example 1 at different points during the reaction.

[0084] Figure 11 Representative TEM images of metal nanomaterials formed in different molar ratios of organic compounds according to Example 2.

[0085] Figure 12 Representative SEM and TEM images of metal nanomaterials formed in different molar ratios according to Example 2.

[0086] Figure 13 : Schematic diagram of metal nanomaterials synthesized according to Example 2 with different molar ratios.

[0087] Figure 14 Representative TEM images and SAED spectra of metal nanosheets formed using sodium dichloroisocyanurate as an organic compound according to Example 3.

[0088] Figure 15 Representative TEM images and SAED spectra of metal nanosheets formed using 4-(dimethylamino)benzoic acid as an organic compound according to Example 4.

[0089] Figure 16 Representative TEM images of single-crystal metal nanoplates of various sizes formed by adding inorganic salts according to Example 5.

[0090] Figure 17 : A schematic diagram of the truncated triangular nanoplate formed according to Example 5. The method of measuring the side length is shown (where the measured value of the side length is the longest of the three main sides).

[0091] Figure 18 Histogram of the dimensions of metal nanoplates formed with different molar ratios according to Example 5.

[0092] Figure 19 Side-view TEM image of a stack of metal nanoplates formed in the presence of inorganic salts at a certain molar ratio according to Example 5.

[0093] Figure 20 AFM images and height analysis of two metal nanoplates formed in the presence of inorganic salts at a certain molar ratio according to Example 5.

[0094] Figure 21 a and Figure 21 b: Top view of the metal nanoplates formed in the presence of inorganic salts at a certain molar ratio according to Example 5 ( Figure 21 a) and lateral gaze ( Figure 21 b) HRTEM image. Figure 21 The small image of a is <111> SAED map in the region axis.

[0095] Figure 21 c: XRD patterns of metal nanoplates formed in the presence of inorganic salts at a certain molar ratio according to Example 5 at 2θ in the range of 30° to 100°.

[0096] Figure 22 SAED pattern of a large metal nanoplate formed in the presence of a high molar ratio of inorganic salt according to Example 5.

[0097] Figure 23 Histograms and average thicknesses of metal nanoplates formed in the presence of inorganic salts at different molar ratios according to Example 5.

[0098] Figure 24 The ultraviolet-visible spectrum of the metal nanoplates formed in the presence of inorganic salts at a certain molar ratio according to Example 5.

[0099] Figure 25 Representative TEM images and SAED spectra of metal nanosheets formed using ethyl orange as an organic compound according to Example 7.

[0100] Figure 26 Representative TEM images and SAED spectra of metal nanosheets formed using p-methyl red as an organic compound according to Example 8.

[0101] Figure 27 Representative TEM images and SAED spectra of metal nanosheets formed using methyl red as an organic compound according to Example 9.

[0102] Figure 28 Representative TEM images and SAED spectra of metal nanosheets formed using 4-methylaminobenzoic acid as an organic compound according to Example 10.

[0103] Figure 29 Representative TEM images and SAED spectra of metal nanosheets formed using 2,2'-bipyridine as an organic compound according to Example 11.

[0104] Figure 30 Representative TEM images, AFM images, side length histograms, and UV-vis spectra of nanoplates formed using NaBr as an inorganic salt according to Example 6. Detailed Implementation

[0105] All reagents used in the examples were commercially available and used directly without further purification. Ultrapure water was used in all experiments, for example... The resistivity at 25℃ is 18.2 MΩ·cm. Before use, the reaction vessel should be cleaned with aqua regia (HNO3:HCl volume ratio 1:3), thoroughly rinsed with ultrapure water, dried in an oven, and then cooled.

[0106] Example 1: Ultrathin gold nanosheets using methyl orange as an organic compound

[0107] synthesis

[0108] At 20°C, 1 mL (5 mM) of aqueous gold chloride (HAuCl4) solution and 0.5 mL (100 mM) of freshly prepared sodium citrate (SC) solution were sequentially added to 4 mL (0.21 mM) of aqueous methyl orange (MO) solution. The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0109] After 12 hours, a blue-green dispersion was obtained. The dispersion remained stable under environmental conditions for more than 15 months. Figure 3 The UV-Vis spectrum of the reaction solution after 12 hours is shown. The UV-Vis spectrum exhibits a broad excitation band in the range of 500 nm to 1300 nm. The absence of a prominent peak near 520 nm indicates the absence of isotropic gold nanoparticles.

[0110] The reaction product was collected by centrifugation at 1000g relative centrifugal force field (RCF) for 10 minutes. The precipitate was then washed several times with water until the supernatant was colorless. The precipitate was then redispersed in water for further analysis.

[0111] Characterization

[0112] Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) images of ultrathin nanosheets were acquired. Bright-field TEM images were obtained using an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm microscope running Aztec software. 2 Images were captured using a Tecnai F20TEM / STEM with an SD detector and a Gatan Orius CCD camera running Digital Micrograph software. Dark-field STEM images were acquired using a FEI Titan3 Themis G2 S / TEM operating at 300 kV, equipped with a monochromator, FEI SuperX EDX detector, Gatan Quantum ER 965 imaging filter, and a Gatan OneView CCD camera running GMS 3.1.

[0113] TEM and STEM samples were prepared by dropping 5 μL of redispersed gold nanosheet solution onto a carbon-coated copper grid (Agar Scientific Ltd.) and allowing it to air dry at room temperature.

[0114] Figure 4 Image a shows a representative bright-field TEM image, demonstrating the high-yield formation of 2D nanosheets. Figure 5Detailed analysis of the TEM images of the 20 individual nanosheets shown indicates that they possess similar fractal dimensions, ranging from 1.69 to 1.78. The fractal dimensions were calculated using FDC software (Paul Bourke, http: / / paulbourke.net / fractals / fracdim / ) by adjusting the image contrast, allowing the algorithm to correctly identify the overall shape of each individual nanosheet.

[0115] Figure 4 Image b is a bright-field TEM image at a higher magnification, showing the curved profile of the nanosheets. This indicates that they are flexible. Figure 4 c is a representative dark-field STEM image, showing the translucent appearance, folded edges, and wrinkles of the nanosheets. This demonstrates their ultrathin nature.

[0116] The thickness of ultrathin gold nanosheets was determined using AFM height measurement. Samples were imaged in air at room temperature on a Dimension FastScan BioAFM (Bruker, Billerica, MA) using a FastScan-A cantilever probe (Bruker, Camarillo, CA) in tapping mode. The accuracy of the Z-piezoelectric calibration was confirmed by measuring the indentation depth of HF-etched mica. The height generated by HF etching was 1.00 nm, representing half the c-axis spacing of a monoclinic cell. HF mica was prepared by reacting freshly cut mica sheets in 40% HF for 4 hours. HF was neutralized with excess sodium bicarbonate and ultrapure water prior to imaging. 2 μL of redispersed gold nanosheet solution was deposited onto freshly cut mica and left at room temperature for water evaporation. Images were typically acquired at a scan rate of 10.5 Hz, a resolution of 2048 × 2048 pixels, and scan sizes ranging from 1 μm to 5 μm. The cantilever is automatically tuned 5% below resonance for operation in tap mode (typical resonance frequency is 1400kHz). Nanosheet height is analyzed using a spectral profile function set to 5 pixel linewidth in Gwyddion software.

[0117] Figure 6 AFM images of nanosheets 1 through 5 are shown, with insets showing the thickness distribution of nanosheets 1 through 3 as measured along the white line shown. The average thicknesses of nanosheets 1 through 5 are 0.50 nm, 0.53 nm, 0.44 nm, 0.48 nm, and 0.50 nm, respectively. Figure 7 Histograms of nanosheet thickness data for 30 nanosheets with an average thickness of 0.42 ± 0.05 nm are shown.

[0118] The crystal structure of the ultrathin nanosheets was investigated using high-resolution transmission electron microscopy (HRTEM), selected area diffraction (SAED), and X-ray diffraction (XRD). HRTEM images were acquired using a FEITitan3 Themis G2S / TEM operated at 300 kV, equipped with a monochromator, a FEI SuperX EDX detector, a Gatan Quantum ER 965 imaging filter, and a Gatan OneView CCD camera running GMS 3.1. SAED spectra were obtained using an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2 camera running Aztec software. 2 Acquisition was performed using a Tecnai F20TEM / STEM with an SD detector and a Gatan Orius CCD camera running Digital Micrograph software. XRD patterns were obtained using a Bruker D8 X-ray diffractometer equipped with a Cu Kα source and an X'cellerator detector. Continuous scans were performed in 2θ ranges from 20° to 90° in steps of 0.05°, with an acquisition time of 1 hour per sample.

[0119] HRTEM and SAED samples were prepared by dropping 5 μL of redispersed gold nanosheet solution onto a carbon-coated copper grid (Agar Scientific Ltd.) and allowing it to air dry at room temperature. XRD samples were prepared by depositing and drying a slurry directly onto a low-background Si sample holder.

[0120] Figure 8 Image a shows an HRTEM image of ultrathin gold nanosheets. The crystal structure of the nanosheets exhibits a 6-fold symmetry structure with a lattice spacing of 0.25 nm. This is consistent with 1 / 3 {422} lattice spacing of fcc gold.

[0121] Figure 8 b shows along <111> SAED spectra of the ultrathin gold nanosheets with a regional axis. The SAED spectra show two sets of six-fold symmetric spots, including strong spots (boxes) identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm) and weak spots (circles) identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). The presence of this forbidden reflection is due to the locally incomplete cubic (ABC) packing and locally hexagonal close packing (hcp) caused by its ultrathin nature.

[0122] Figure 8c shows the XRD pattern of the ultrathin gold nanosheets. The XRD pattern shows a main (111) peak at 38.2°, indicating that... <111> Oriented fcc Au crystals dominate in the nanosheet sample. In addition to the main Bragg reflection of fcc Au, shoulder peaks at approximately 37° and approximately 40° correspond to the (002) and (101) lattice spacings of the Au hcp phase, respectively.

[0123] Both HRTEM and SAED results showed the single-crystal properties of Au nanosheets and <111> Orientation. Therefore, based on the thickness measured by AFM, the Au nanosheets contain 2 to 3 Au atomic layers.

[0124] The growth mechanism of ultrathin Au nanosheets was investigated by characterizing the reaction products at different stages of the reaction using TEM and UV-vis. TEM images were acquired using a Tecnai G2 Spirit TWIN / BioTWIN at an accelerating voltage of 120 kV. TEM samples were prepared as described above for other measurements. UV-Vis spectra were recorded using a PerkinElmer UV / VIS / NIR Lambda 19 spectrophotometer.

[0125] Figure 9 a, Figure 9 b and Figure 9 c shows TEM images of the reaction products after 2, 10, and 20 minutes of reaction (the reaction initiation point is defined as the addition of sodium citrate). The product collected at 2 minutes includes nanosheets of different lateral sizes. This indicates that 2D Au nanostructures form in the early stages of the reaction. SAED spectra collected after 2 minutes of reaction ( Figure 9 The small image (a) shows that these nanosheets are <111> Orientation.

[0126] Figure 10 The UV-Vis spectra of the reaction mixture collected at different points during the reaction are shown. The UV-Vis spectra show broad absorption in the near-infrared (NIR) region and a shoulder peak near 550 nm, confirming the formation of anisotropic nanostructures consistent with TEM observations.

[0127] As reaction time increases ( Figure 9 (b) and (9c), the lateral dimensions of the product increase, and the shape exhibits a branching, irregular structure. Figure 10 In the UV-Vis spectrum, the absorption in the NIR region gradually increases, reaching its maximum at approximately 12 hours. This indicates that the reaction is complete. Figure 5 The fractal dimension of the nanosheets shown is close to 1.71, indicating that the nanosheets are formed through a diffusion-restricted aggregation pathway.

[0128] Example 2: Synthesis of different nanostructures by changing the molar ratio of organic compounds to noble metal ion sources Structure

[0129] synthesis

[0130] At 20°C, 1 mL of aqueous solution of gold chloride (HAuCl4), 5 mM, and 0.5 mL of freshly prepared sodium citrate (SC), 100 mM, were sequentially added to an aqueous solution of methyl orange (MO), 4 mL, with different concentrations (see Table 1). The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0131] Twelve hours later, the product was collected by centrifugation at 1000g relative centrifugal force field (RCF) for 10 minutes. The precipitate was then washed several times with water until the supernatant was colorless. The precipitate was then redispersed in water for further analysis.

[0132] Characterization

[0133] TEM images of the reaction products at different molar ratios were captured. TEM samples were prepared as described in Example 1. TEM images were obtained using an Oxford Instruments 80mm f / 200 MHz field emission gun with a 4.5 kV extraction voltage and running Aztec software, operating at an accelerating voltage of 200 kV. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image.

[0134] Figure 11 It shows that with 0.000 ( Figure 11 a) 0.056 Figure 11 b) and 0.112 ( Figure 11 c) Representative TEM images of different nanostructures formed at lower molar ratios. Figure 12 It shows that at 0.56 ( Figure 12 b), 0.672 Figure 12 d) and 2( Figure 12 Representative TEM images of different nanostructures formed at higher molar ratios (f).

[0135] Scanning electron microscopy (SEM) images of the reaction products formed at different molar ratios were acquired using a Hitachi SU8230 at 2 kV. Individual SEM samples were prepared by placing 5 μL of the redispersible solution on an aluminum substrate and allowing it to air dry at room temperature.

[0136] Figure 12 This shows that at a molar ratio of 0.56 ( Figure 12 a) 0.672 Figure 12 c) and 2( Figure 12 Representative SEM images of different nanostructures formed under condition e).

[0137] Table 1 is based on Figure 11 and Figure 12 The corresponding TEM and SEM images shown summarize the types of nanomaterials formed at different molar ratios. Schematic diagrams of the products synthesized at different molar ratios are shown below. Figure 13 .

[0138] Table 1: Types of nanostructures formed at different molar ratios

[0139]

[0140] Example 3: Synthesis of metal nanostructures using sodium dichloroisocyanurate

[0141] synthesis

[0142] Unlike methyl orange, sodium dichloroisocyanurate has only one aromatic ring (see [link to product description]). Figure 2 However, it still possesses a rigid aromatic portion as well as hydrophilic and hydrophobic portions.

[0143] At 20°C, 1 mL (5 mM) of aqueous solution of gold chloride (HAuCl4) and 0.5 mL (100 mM) of freshly prepared sodium citrate (SC) aqueous solution were sequentially added to 4 mL (0.21 mM) of sodium dichloroisocyanurate aqueous solution. The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0144] Twelve hours later, the reaction product was collected by centrifugation at 1000g relative centrifugal force field (RCF) for 10 minutes. The precipitate was then washed several times with water until the supernatant was colorless. The precipitate was then redispersed in water for further analysis.

[0145] Characterization

[0146] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 14 b and Figure 14 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 14The TEM image shown in figure a was acquired using a Tecnai G2 spirit TWIN / BioTWIN at an accelerating voltage of 120 kV. Figure 14 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm laser running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0147] Figure 14 a to Figure 14 c shows bright-field TEM images of metal nanostructures formed using sodium dichloroisocyanurate as an organic compound at different magnifications. These figures demonstrate that 2D metal nanostructures are formed in high yields when using different organic compounds that meet the requirements of this invention. Figure 14 d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as described in Example 1. These results show that similar ultrathin metal nanosheets can be formed using sodium dichloroisocyanurate at the same molar ratio as methyl orange (Example 1).

[0148] Example 4: Synthesis of metal nanostructures using 4-(dimethylamino)benzoic acid

[0149] synthesis

[0150] At 20°C, 1 mL (5 mM) of aqueous gold chloride (HAuCl4) and 0.5 mL (100 mM) of freshly prepared sodium citrate (SC) aqueous solution were sequentially added to 4 mL (0.32 mM) of aqueous 4-(dimethylamino)benzoic acid. The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0151] Twelve hours later, the reaction product was collected by centrifugation at 1000g relative centrifugal force field (RCF) for 10 minutes. The precipitate was then washed several times with water until the supernatant was colorless. The precipitate was then redispersed in water for further analysis.

[0152] Characterization

[0153] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 15 a to Figure 15 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 15 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0154] Figure 15 a to Figure 15 c shows bright-field TEM images of metal nanostructures formed using 4-(dimethylamino)benzoic acid as an organic compound at different magnifications. These figures demonstrate that 2D metal nanostructures are formed in high yield when using an azo-free organic compound that meets the requirements of this invention. Figure 15 d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as described in Example 1. These results show that ultrathin metal nanosheets similar to those in Examples 1 to 3 can be formed using non-azo compounds such as 4-(dimethylamino)benzoic acid.

[0155] Example 5: Synthesis of metal nanoplates controlled by introducing FeBr3

[0156] synthesis

[0157] At 20°C, freshly prepared ferric bromide (FeBr3) aqueous solution (1 mL, different concentrations, see Table 2), gold chloride (HAuCl4) aqueous solution (1 mL, 5 mM), and freshly prepared sodium citrate (SC) aqueous solution (0.5 mL, 100 mM) were sequentially added to methyl orange (MO) aqueous solution (3 mL, 0.28 mM). The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0158] After reacting for 12 hours at a molar ratio of inorganic salt to noble metal ion source ≤ 0.252, the reaction product was collected by centrifugation at 3000g relative centrifugal force field (RCF) for 10 minutes. The precipitate was washed several times with water until the supernatant was colorless. The precipitate was then redispersed in water for further analysis.

[0159] After reacting for 12 hours at a molar ratio of inorganic salt to noble metal ion source >0.252, the reaction product precipitated at the bottom of the vial. After removing the supernatant, the product was dispersed in water and washed twice by centrifugation at 1000g RCF for 8 minutes. The product was then redispersed in water for further analysis.

[0160] Characterization

[0161] The reaction products were analyzed by TEM. TEM samples were prepared as described in Example 1. TEM images were obtained using an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm microscope running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image.

[0162] Figure 16 Representative TEM images of nanoplates produced with FeBr3 at different molar ratios are shown. The specific concentrations of FeBr3 used in each sample are shown in Table 2.

[0163] Table 2 summarizes the average side lengths (measured by TEM) of nanoplates produced using inorganic salts with different molar ratios. Figure 17 It defines how to measure the side length of each nanoplate. Figure 18 Histograms of nanoplate lengths with different molar ratios are shown.

[0164] Table 2: Average side length of nanoplates formed from FeBr3 with different molar ratios

[0165]

[0166] For inorganic salts with a specific molar ratio, the thickness of the nanoplates was also measured by TEM imaging and / or AFM. The preparation and measurement of AFM samples were performed as described in Example 1.

[0167] Figure 19 A side-view TEM image of a stack of nanoplates formed with a FeBr3 molar ratio of 0.126 is shown. Figure 19 Direct thickness measurements yielded a nanoplate thickness of 6.2 ± 0.3 nm (excluding the observable organic capping layer). Figure 20 AFM images of two nanoplates formed at a FeBr3 molar ratio of 0.126 are shown. Along... Figure 20 The height curve of the red line is shown in the inset. AFM analysis indicates that the top and bottom surfaces are flat at the atomic level, with a thickness of 7.5 ± 0.4 nm. AFM measurements include the organic coating layer, which is not included in TEM analysis.

[0168] The crystal structure of the nanoplates formed with a FeBr3 molar ratio of 0.126 was investigated by HRTEM, SAED, and XRD analysis. The preparation and measurement of the HRTEM, SAED, and XRD samples were performed as described in Example 1.

[0169] Figure 21 Image a shows a TEM image of the top surface of the metal nanoplate. The spacing between each set of white parallel lines was measured to be approximately 0.25 nm, corresponding to 1 / 3 of the {422} lattice spacing of fcc-gold. The inset image shows... <111> SAED pattern in the region axis. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm). Weak spots (circles) are identified as prohibited 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm).

[0170] Figure 21 b shows a TEM image of the side surface of the metal nanoplate. The spacing between each set of white parallel lines was measured to be approximately 0.24 nm, corresponding to the {111} crystal plane spacing of fcc-gold. This indicates that the side surface of the nanoplate includes {111} crystal planes. Figure 21 a and 21b indicate that the nanoplate is <111> Oriented gold single crystals.

[0171] Figure 21 c shows the XRD pattern of the nanoplates formed with a FeBr3 molar ratio of 0.126. The XRD pattern shows only {111} peaks. This indicates that the nanoplates are... <111> Oriented gold single crystals.

[0172] Micron-sized nanoplates formed from inorganic salts at high molar ratios also exhibit single crystallinity with {111} domains and atomically flat surfaces. Nanoplates with sizes of approximately 1 μm and 2 μm (respectively) were observed in the SAED spectrum. Figure 22 a and Figure 22 b) Take the forbidden 1 / 3{422} reflection as an example.

[0173] In addition to size, the thickness of the formed metal nanoplatelets can also be controlled by changing the molar ratio of inorganic salts. Figure 23 a to Figure 23 d is a histogram of the thickness of the metal nanoplate (measured by AFM), with average lengths of... Figure 23 a 148nm, Figure 23 b 193nm Figure 23 c approximately 1μm and Figure 23 The diameter (d) is approximately 2 μm. The average height of the nanoplates increases with increasing molar ratio of inorganic salts.

[0174] The gold nanoplates prepared in this way exhibit localized surface plasmon resonance (LSPR) features. These LSPR features correspond to different dipole and quadrupole plasmon resonances at 1100 nm and 750 nm in the UV-Vis spectrum, respectively. Figure 24 Here is an example of the UV-Vis spectrum of a metal nanoplate with an average length of 148 nm, showing these characteristics.

[0175] Example 6: Synthesis of metal nanoplates controlled by introducing NaBr

[0176] The synthesis method was as described in Example 5, using an aqueous NaBr solution (1 mL, 1.89 mM) instead of an aqueous ferric(III) bromide solution. This corresponds to a molar ratio of 0.378 between sodium bromide and the noble metal ion source.

[0177] The reaction products were analyzed by TEM. TEM samples were prepared as described in Example 1. TEM images were obtained using an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm microscope running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image.

[0178] Figure 30 a and Figure 30 b shows a representative TEM image of the nanoplates produced in the presence of NaBr. The side lengths of the nanoplates were measured as described in Example 5. Figure 30 c shows a histogram of the side lengths measured from the TEM image, indicating an average side length of 150 ± 7 nm.

[0179] Thickness measurements using TEM and AFM were performed as described in Example 5. AFM sample preparation and measurement were performed as described in Example 1.

[0180] Figure 30 Figure d shows a side-view TEM image of a stack of nanoplates formed at a NaBr molar ratio of 0.378. Figure 30 Direct thickness measurements of d yielded a nanoplate thickness of approximately 10 nm (excluding the observable organic capping layer). Figure 30 e shows AFM images of two nanoplates formed at a NaBr molar ratio of 0.378. Along Figure 30 The height curve of the red line for e is shown in the inset. AFM analysis indicates that the top and bottom surfaces are flat at the atomic level, and the nanoplate thickness is between 9 and 10 nm, which is very consistent with the TEM images. The AFM measurements include the organic coating layer, which is not included in the TEM analysis.

[0181] The gold nanoplates prepared in this way exhibit localized surface plasmon resonance (LSPR) features. These LSPR features correspond to different dipole and quadrupole plasmon resonances at 1100 nm and 750 nm in the UV-Vis spectrum, respectively. Figure 30 f shows the UV-Vis spectrum of the metal nanoplates produced with a NaBr molar ratio of 0.378, revealing these characteristics.

[0182] These results demonstrate that LSPRs with controllable size and thickness of noble metal nanoplatelets can also be produced using different inorganic salts.

[0183] Example 7: Synthesis of Metal Nanostructures Using Ethyl Orange

[0184] The synthesis method is as described in Example 3, using an aqueous solution of ethyl orange (4 mL, 0.21 mM) instead of an aqueous solution of sodium dichloroisocyanurate.

[0185] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 25 a to Figure 25 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 25The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0186] Figure 25 a to Figure 25 c shows a bright-field TEM image of high-yield formation of 2D metal nanostructures using ethyl orange. Figure 25 d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as shown in Example 1. These results show that similar ultrathin metal nanosheets can be formed using ethyl orange in the same molar ratio as methyl orange (Example 1).

[0187] Example 8: Synthesis of Metal Nanostructures Using p-Methyl Red

[0188] The synthesis method is as described in Example 3, using an aqueous solution of p-methyl red (4 mL, 0.21 mM) instead of an aqueous solution of sodium dichloroisocyanurate.

[0189] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 26 a to Figure 26 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 26 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0190] Figure 26 a to Figure 26 c shows a bright-field TEM image of the high-yield formation of 2D metal nanostructures using p-methyl red (4 mL, 0.21 mM). Figure 26 d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as shown in Example 1. These results show that similar ultrathin metal nanosheets can be formed using an aqueous solution of p-methyl red with the same molar ratio as methyl orange (Example 1).

[0191] Example 9: Synthesis of Metal Nanostructures Using Methyl Red

[0192] The synthesis method is as described in Example 3, using an aqueous solution of methyl red (4 mL, 0.21 mM) instead of an aqueous solution of sodium dichloroisocyanurate.

[0193] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 27 a to Figure 27 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 27 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0194] Figure 27 a to Figure 27 c shows bright-field TEM images of the high-yield formation of 2D metal nanostructures using an aqueous methyl red solution at different magnifications. Figure 27d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as shown in Example 1. These results show that similar ultrathin metal nanosheets can be formed using an aqueous solution of methyl red with the same molar ratio as methyl orange (Example 1).

[0195] Example 10: Synthesis of Metal Nanostructures Using 4-Methylaminobenzoic Acid

[0196] The synthesis method is as described in Example 3, using an aqueous solution of 4-methylaminobenzoic acid (4 mL, 0.21 mM) instead of an aqueous solution of sodium dichloroisocyanurate.

[0197] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 28 a to Figure 28 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 28 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2 Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0198] Figure 28 a to Figure 28 c shows bright-field TEM images of metal nanostructures formed using 4-methylaminobenzoic acid as an organic compound at different magnifications. These figures demonstrate that 2D metal nanostructures are formed in high yields when using different organic compounds that meet the requirements of this invention. Figure 28d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as shown in Example 1. These results show that similar ultrathin metal nanosheets can be formed using an aqueous solution of 4-methylaminobenzoic acid with the same molar ratio as methyl orange (Example 1).

[0199] Example 11: Synthesis of metal nanostructures using 2,2'-bipyridine

[0200] Ideal features for selecting organic compounds suitable for this invention include the presence of hydrogen bonding and aromatic interactions in both axial directions. These features contribute to the 2D planar stacking required to create closed spaces. Based on these criteria, 2,2'-bipyridine was also selected as a candidate compound.

[0201] At 20°C, 1 mL (5 mM) of aqueous gold chloride (HAuCl4) and 0.5 mL (100 mM) of freshly prepared sodium citrate (SC) aqueous solution were sequentially added to 4 mL (0.21 mM) of aqueous 2,2'-bipyridine. The resulting reaction mixture was allowed to stand at 20°C for 12 hours.

[0202] After 12 hours, a precipitate formed at the bottom of the vial. The supernatant was removed, and the product was then redispersed in ultrapure water. The product was then washed twice by centrifugation at 1000 g RCF for 8 minutes. The precipitate was then redispersed in water for further analysis.

[0203] TEM images and SAED spectra of the reaction products were captured. The TEM and SAED samples were prepared as described in Example 1. Figure 29 a to Figure 29 The TEM image shown in c was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm f / 2.0T sensor running Aztec software. 2 SD detector and Gatan Orius CCD camera running Digital Micrograph software, Tecnai F20 TEM / STEM image. Figure 29 The SAED spectrum shown in d was obtained by operating at an accelerating voltage of 200 kV, equipped with a field emission gun using a 4.5 kV extraction voltage, and an Oxford Instruments 80mm receiver running Aztec software. 2Tecnai F20 TEM / STEM acquisition using an SD detector and a Gatan Orius CCD camera running Digital Micrograph software.

[0204] Figure 29 a to Figure 29 c shows bright-field TEM images of metal nanostructures formed using 2,2'-bipyridine as an organic compound at different magnifications. These figures demonstrate that 2D metal nanostructures are formed in high yields when using different organic compounds with different structures that meet the requirements of this invention. Figure 29 d shows along <111> SAED pattern of the axial metallic nanostructure. Strong spots (boxes) are identified as allowed {220} Bragg reflections (corresponding to a lattice spacing of 0.144 nm), while weak spots (circles) are identified as forbidden 1 / 3 {422} reflections (corresponding to a lattice spacing of 0.250 nm). This indicates the presence of atomically flat surfaces. <111> Oriented 2D gold nanostructures, as shown in Example 1. These results show that similar ultrathin metal nanosheets can be formed using 2,2'-bipyridine with the same molar ratio as methyl orange (Example 1).

Claims

1. A method for preparing noble metal nanomaterials, comprising: (A) An aqueous solution of a noble metal ion source and a reducing agent are added to an aqueous solution of an organic compound to form a reaction mixture, wherein the organic compound is an organic amphiphilic molecule capable of 2D planar stacking in aqueous solution, and the organic compound has the following molecular formula: in: R is hydrogen or C. n H 2n+1 Partial, where 0 < n ≤ 6; R' is C m H 2m+1 Partial, where 0 < m ≤ 6; Z is a bond or a diazenyl or diazenylbenzene linkage; and Y is a moiety containing a carboxyl group, a carbonyl group, a hydroxyl group, an acid anhydride group, an amino group, an amide group, a thiol group, or a sulfonyl group; and (B) Separate the noble metal nanomaterial from the reaction mixture.

2. The method according to claim 1, wherein the nanomaterial is characterized by the presence of nanosheets.

3. The method according to claim 2, wherein the thickness of the nanosheet, as measured by atomic force microscopy (AFM), is not greater than 6 times the atomic radius of the noble metal.

4. The method of claim 2, wherein the thickness of the nanosheet, as measured by atomic force microscopy (AFM), is no more than 3 atomic layers.

5. The method according to claim 2, wherein the average thickness of the nanosheet is in the range of 0.40 nm to 0.50 nm.

6. The method according to claim 1, wherein the nanomaterial is characterized by the presence of nanoplates.

7. The method according to any one of the preceding claims, wherein the precious metal is Au.

8. The method according to any one of claims 1-6, wherein the organic compound is selected from methyl orange, ethyl orange, p-methyl red, methyl red, sodium dichloroisocyanurate, 4-(dimethylamino)benzoic acid and 4-methylaminobenzoic acid.

9. The method according to any one of claims 1-6, wherein the molar ratio of the organic compound to the noble metal ion source in the reaction mixture is in the range of 0.10 to 0.

5.

10. The method according to any one of claims 1-6, further comprising: (A') An aqueous solution of an inorganic salt is added to the reaction mixture.

11. The method according to claim 10, wherein the molar ratio of the inorganic salt to the noble metal ion source in the reaction mixture is in the range of 0.1 to 0.8.

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