Wet chemical method for selectively etching specific exposed crystal face of gold nanomaterial

Abstract

The invention discloses a wet chemical method for selectively etching a specific exposed crystal face of a gold nano material, and belongs to the field of controllable synthesis of nano materials. Comprising the following steps: sequentially adding a chloroauric acid solution, a chloroplatinic acid solution, a potassium iodide solution, a hydrochloric acid solution and an ascorbic acid solution into a cetyltrimethylammonium bromide (CTAB) solution, then adding a gold nanocrystal seed solution into the mixed solution, uniformly mixing, standing for reaction under a certain temperature condition, filtering, washing, and drying to obtain the gold nanocrystal. The gold nano material with the regular-shape etching recess is obtained; according to the selective etching method for the gold nanomaterial, selective controllable etching of the specific crystal face of the gold nanomaterial can be achieved only through one step, an etching pit in a regular shape is formed in the crystal face of the gold nanomaterial hexagonal plate (111), and the problems that in the prior art, wet chemical etching is high in randomness, and the shape of an etching part is irregular and uncontrollable are solved.

Description

Technical Field

[0001] The present invention relates to a wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials, and this etching method can be applied to the field of controllable synthesis of gold nanomaterials. Background Art

[0002] Noble metal plasmonic nanoparticles have been widely used in the fields of optics, sensing, catalysis, and biomedical science because they can strongly interact with light. Their optical properties can be changed by the composition, size, morphological structure of the particles, and the surrounding medium. For example, the plasmon resonance wavelength of gold nanorods can shift with the change of their aspect ratio. So far, most of the reported gold nanoparticles prepared by wet chemical methods have regular shapes, such as spherical, rod-shaped, biconical, plate-shaped, octahedral, and icosahedral. Since the properties of gold nanoparticles are closely related to their structural morphology, breaking the regularity, introducing complexity and designability in their structure can endow gold nanomaterials with novel properties that cannot be achieved by regular morphologies. For example, the use of left-handed and right-handed amino acids and polypeptide molecules can induce the three-dimensional chiral helical growth of gold nanostructures, thereby endowing them with chiral properties (Nature, 2018, 556, 360–365). The chemical synthesis of asymmetric gold nanocups can be achieved by the sacrificial template method, and gold nanocups have strong magnetic plasmon resonance modes due to their special ring-opening structure (Adv. Mater. 2016, 28, 6322).

[0003] It can be seen that breaking the structural symmetry and regularity of nanoparticles has great development potential in the field of controllable synthesis of nanomaterials. However, it is quite challenging to break the symmetric growth law of nanostructures in the field of wet chemical synthesis because breaking symmetric growth conflicts with the principle of energy minimization in the chemical synthesis process. Therefore, researchers have strived to design and develop a series of synthesis methods that can prepare gold nanomaterials with special configurations, such as local surface protection growth method, template synthesis method, molecular-induced overgrowth and etching method, etc. The above-mentioned wet chemical methods usually involve multiple steps, and the cumbersome synthesis or etching process greatly limits the expansion of the morphology of the gold nanomaterial library, thus hindering the development of the performance and applications of gold nanomaterials.

[0004] Taking the etching method as an example, the gold nanomaterials prepared by wet chemical etching method disclosed in existing literature or patents (Applied Materials Today, 2021, 22, 100940; Patent CN 112296352 B) mainly etch irregular disordered structures on the surface or inside of the gold nanomaterials, so that they can be used for the loading and delivery of anti-tumor or antibacterial drugs. This reported etching method has uncontrollable etching positions for gold nanoparticles and strong randomness. In addition, its etching notches are also in irregular shapes, making it difficult for the special configuration gold nanoparticles prepared by the etching method to have strong collective properties, thus affecting the application and transformation of the nanoparticles prepared by the etching method. Summary of the Invention

[0005] The purpose of the present invention is to provide a wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials. This wet chemical etching method can achieve (1) the growth of gold nanomaterials and (2) the selective and controllable etching of the exposed crystal planes of gold nanomaterials in only one step. Finally, a regularly shaped etching depression appears on the gold nanomaterials, and the size of the etched part can be adjusted by adjusting the reaction time, breaking through the bottlenecks of traditional chemical etching methods such as randomness, irregularity, and uncontrollability.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials, characterized by comprising the following steps: successively adding chloroauric acid solution, chloroplatinic acid solution, potassium iodide solution, hydrochloric acid solution and ascorbic acid solution into cetyltrimethylammonium bromide (CTAB) solution, then adding gold nanoseed solution into the above mixed solution and mixing evenly, and standing and reacting under certain temperature conditions to obtain gold nanomaterials with regularly shaped etching depressions.

[0008] The mechanism of action of the present invention is as follows:

[0009] In the present invention, we developed a simple wet chemical etching method. By combining seed-mediated growth and iodine ion-induced Pt(IV) etching in the same step, we successfully achieved the selective and controllable etching of specific exposed crystal planes of gold nanomaterials. Finally, a regularly shaped etching depression appears on the specific exposed crystal plane, and the size of the etched part can be adjusted by adjusting the reaction time. This wet chemical etching method realizes the selective etching of specific crystal planes of nanocrystals, breaks through the bottlenecks of chemical etching methods such as randomness, irregularity, and uncontrollability, and is also innovative in the preparation method.

[0010] Further settings are as follows:

[0011] The chloroauric acid solution is the growth source of the gold nanomaterial, ascorbic acid is the reducing agent, the potassium iodide solution is the assistant for inducing etching to occur on the (111) crystal plane of the gold nanomaterial, chloroplatinic acid is the etching agent, and the hydrochloric acid solution is the pH regulator of the mixed solution.

[0012] According to the added molar ratio, the CTAB solution: chloroauric acid solution: chloroplatinic acid solution: potassium iodide solution: ascorbic acid solution is 2500 - 5000: 5 - 15: 1 - 5: 2 - 10: 30 - 60.

[0013] The pH value of the reaction solution is controlled at 5.0 - 6.8, the reaction temperature is 55°C - 85°C, and the reaction time is 6 - 48 h.

[0014] The gold nanoseeds can be selected from any one of single crystal type, polycrystalline type and twin crystal type, and preferably gold nanodisc seeds (one kind of twin crystal type).

[0015] Preferably, the gold nanoseed solution is a gold nanodisc seed solution, and its extinction peak is at 680 - 880 nm, and the absorbance is 0.5 - 7.

[0016] The volume ratio of the gold nanodisc seed solution to the reaction mixed solution is 1 - 5: 210 - 216.

[0017] Furthermore: When the gold nanodisc seed solution is just added to the reaction mixed solution, the solution is light pale yellow. After shaking and mixing for more than ten seconds, it is placed in an oven and left to react. The solution gradually turns light pale purple. Subsequently, the nanoparticles gradually sink to the bottom of the test tube as the standing time extends, and the solution becomes clear, transparent and colorless.

[0018] The gold nanoseeds described in the present invention can be prepared by the methods already reported in the prior art. For example, the preparation method of gold nanodiscs can refer to the method in the literature (Jiapeng Zheng, Christina Boukouvala, George R. Lewis, Yicong Ma, Yang Chen, Emilie Ringe, Lei Shao, Zhifeng Huang, Jianfang Wang. Halide-assisted differential growth of chiral nanoparticles with threefold rotational symmetry. Nature Communications, 2023, 14: 3783.).

[0019] The gold nanomaterials with regularly shaped etched depressions prepared by the wet chemical etching method of the present invention can be any one of gold nanohexagonal plates, gold nanotriangular plates, gold nanocircular plates, gold nanodecahedrons, etc.

[0020] Specifically preferably: Prepare a gold nanohexagonal plate with selectively etched surface, characterized in that: its morphology is a hexagonal plate, and there is a regularly shaped etched depression on its (111) crystal plane. The etched depression is triangular, and the etched area can be adjusted with the reaction time.

[0021] Compared with the prior art, the beneficial effects of the present invention include:

[0022] (1) In the present invention, the wet chemical preparation method for selectively etching specific exposed crystal planes of gold nanomaterials. Its prominent innovation lies in combining seed-mediated growth and iodine ion-induced Pt(IV) etching in the same step, successfully realizing the selective and controllable etching of gold nanomaterials. Finally, a regularly shaped etched depression appears on a specific crystal plane of the gold nanomaterials, and the size of the etched part can be adjusted by adjusting the reaction time. This preparation method breaks through the bottlenecks of traditional chemical etching methods such as randomness, irregularity, and uncontrollability.

[0023] (2) This wet chemical etching method can realize the growth of gold nanomaterials and the selective and controllable etching of gold nanomaterials in only one step. Finally, the gold nanomaterials have a regularly shaped etched depression, which can be used for the loading and delivery of anti-tumor or antibacterial drugs.

[0024] (3) The present invention has low requirements for experimental instruments, the method is simple and easy to operate, and the obtained etched nanoparticles have a high yield, uniform size, and good dispersibility.

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0026] Figure 1 Transmission electron microscope image (a) and extinction spectrum (b) of the gold nanodisk seeds used in Example 1 of the present invention

[0027] Figure 2 Scanning electron microscope image of a single particle (left) and its structural schematic diagram (right) of the product prepared in Example 1 of the present invention, with the scale bar being 100 nm.

[0028] Figure 3 Scanning electron microscope images of the product prepared in Example 1 of the present invention at different magnifications, magnified 20,000 times (left) and magnified 37,000 times (right).

[0029] Figure 4 Extinction spectrum of the product prepared in Example 1 of the present invention.

[0030] Figure 5 It is the transmission electron microscope energy spectrum diagram of the product prepared in Example 1 of the present invention.

[0031] Figure 6 It is the scanning electron microscope picture of the products obtained at different reaction times in the substitution example of the present invention, and the scale bar is 100 nm.

[0032] Figure 7 It is the scanning electron microscope picture of the product obtained after the etching agent chloroplatinic acid solution was not added in Comparative Example 1 of the present invention, and the scale bar is 100 nm.

[0033] Figure 8 It is the scanning electron microscope picture of the product obtained after the induction assistant potassium chloroiodide solution was not added in Comparative Example 2 of the present invention, and the scale bar is 200 nm. Detailed implementation manners

[0034] The following examples provide those of ordinary skill in the art with how to make and evaluate the present invention. The examples are only illustrative of the present disclosure and do not delimit the scope of limitation. Although efforts have been made to ensure the accuracy of numerical values (e.g., amounts, temperatures, etc.), some errors and deviations should be considered. Unless otherwise stated, the temperature is in °C or at ambient temperature.

[0035] Example 1: Selective etching of the (111) crystal plane of gold nanohexagonal plates

[0036] 200 μL of 0.01 M chloroauric acid solution, 100 μL of 0.01 M chloroplatinic acid solution, 20 μL of 0.02 M potassium iodide solution, 250 μL of 1 M hydrochloric acid solution and 80 μL of 0.1 M ascorbic acid solution were successively added to 10 mL of 0.05 M CTAB solution, and the mixture was shaken evenly until the solution became very light yellow. Subsequently, 250 μL of a gold nanodisk solution with an absorbance of 0.7 (the extinction peak position of the gold nanodisk is at 700 nm) was added to the above mixed solution ( Figure 1 ), shaken well, and allowed to stand and react at 80 °C for 24 h. After centrifugation and concentration, gold nanohexagonal plates with selectively etched surfaces can be obtained.

[0037] Product confirmation:

[0038] The scanning electron microscope pictures of the gold nanohexagonal plates with selectively etched surfaces prepared in Example 1 are as shown in Figure 2 、 3 . There is a regular etching depression on the (111) crystal plane of the gold nanohexagonal plate, and most of the etched areas are regular triangles. The extinction spectrum of the gold nanohexagonal plate with a selectively etched surface is as shown in Figure 4As shown, its main surface plasmon resonance peak is located at 1480 nm, belonging to the second near-infrared band. The elemental composition of the gold nanohexagonal plates with selectively etched surfaces can be observed from Figure 5 It can be seen that only Au element exists in the formal sample itself. A small amount of carbon element is the residue of the carbon support film required for taking transmission electron microscopy, and it does not come from the sample itself.

[0039] Replacement Examples 1-1 to 1-6: Controllable adjustment of the etched area on the surface of gold nanohexagonal plates

[0040] The preparation method is the same as that in Example 1, except that: the reaction time in Example 1 is changed, and the reaction is allowed to stand for 2, 4, 6, 8, 24, and 26 h respectively at 80 °C. After centrifugation, it is concentrated to obtain gold nanohexagonal plates etched for different periods of time, so as to study the influence of the reaction time on the etched area. The specific parameters are shown in Table 1.

[0041] Table 1: Influence of reaction time on product performance

[0042]

[0043]

[0044] Analysis:

[0045] As Figure 6 shown, when the reaction time is 2 h, only complete gold nanohexagonal plates grow from the gold nanodisk seeds, and no etching occurs; when the reaction time is 4 h, slight etching appears on the surface of the gold nanohexagonal plates, but no triangular etching depressions appear; when the reaction time reaches 6 h, triangular etching appears on the (111) crystal plane of the gold nanohexagonal plates, and as the reaction time prolongs, the triangular etching area gradually increases.

[0046] Comparative Example 1: Product after not adding chloroplatinic acid solution to the reaction system

[0047] To confirm the role of chloroplatinic acid as an etchant in the reaction system, we conducted the following control experiment:

[0048] 200 μL of 0.01 M chloroauric acid solution, 20 μL of 0.02 M potassium iodide solution, 250 μL of 1 M hydrochloric acid solution, and 80 μL of 0.1 M ascorbic acid solution were successively added to 10 mL of 0.05 M CTAB solution, and shaken evenly until the solution became very light yellow. Subsequently, 250 μL of a gold nanodisk solution with an absorbance of 0.7 (the extinction peak position of the gold nanodisk is at 700 nm) was added to the above mixed solution, shaken well, and allowed to stand and react at 80 °C for 24 h. After centrifugation, it was concentrated to obtain the reaction product, as shown in the appendix Figure 7 . From Figure 7It can be seen that triangular etching depressions do not appear on the surface of the gold nanometer hexagonal plates, confirming that chloroplatinic acid acts as an etchant in the reaction system.

[0049] Comparative Example 2: The product after not adding potassium iodide solution to the reaction system

[0050] 200 μL of 0.01 M chloroauric acid solution, 100 μL of 0.01 M chloroplatinic acid solution, 250 μL of 1 M hydrochloric acid solution, and 80 μL of 0.1 M ascorbic acid solution were successively added to 10 mL of 0.05 M CTAB solution. After shaking evenly until the solution became very light pale yellow, 250 μL of a gold nanodisc solution with an absorbance of 0.7 (the extinction peak position of the gold nanodisc was at 700 nm) was added to the above mixed solution, shaken well, and allowed to stand and react at 80 °C for 24 h. After centrifugation and concentration, the reaction product was obtained. See the appendix Figure 8 . From Figure 8 It can be seen that the product is a plate-like product with irregular edges. The uneven edges should be caused by etching, which confirms the role of potassium iodide solution in calibrating the etched crystal planes in the reaction system, so as to achieve the selective etching of the (111) crystal plane.

[0051] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the present invention patent. For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials, characterized in that, The following steps are involved: Chloroauric acid solution, chloroplatinic acid solution, potassium iodide solution, hydrochloric acid solution and ascorbic acid solution are added to hexadecyltrimethylammonium bromide (CTAB) solution in sequence, and then the gold nanocrystal seed solution is added to the mixed solution and mixed evenly, and the mixture is allowed to react at a certain temperature to obtain a gold nanomaterial with regularly shaped etched depressions.

2. The wet chemical method for selectively etching a specific exposed crystal plane of a gold nanomaterial according to claim 1, characterized in that: According to the added molar ratio, the CTAB solution: chloroauric acid solution: chloroplatinic acid solution: potassium iodide solution: ascorbic acid solution is 2500-5000: 5-15: 1-5: 2-10: 30-60.

3. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 1, characterized in that: The pH value of the reaction solution is controlled at 5.0-6.

8.

4. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 1, characterized in that: The reaction temperature is 55°C to 85°C.

5. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 1, characterized in that: The reaction time is 6 to 48 hours.

6. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 1, characterized in that: The added gold nanocrystal seeds are selected from any one of single crystal, polycrystalline and twin crystal, and the volume ratio of the gold nanocrystal seed solution to the reaction mixed solution is 1-5:210-216.

7. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 6, characterized in that: The added gold nanocrystal seeds are gold nanodisks, and the extinction peak of the gold nanodisk seed solution is at 680-880nm, and the absorbance is 0.5-7.

8. A wet chemical method for selectively etching specific exposed crystal planes of gold nanomaterials according to claim 1, characterized in that: The chloroauric acid solution is a gold source for the growth of gold nanomaterials, ascorbic acid is a reducing agent, potassium iodide solution is an auxiliary agent for inducing etching on the (111) crystal surface of the gold nanomaterial, chloroplatinic acid is an etchant, and hydrochloric acid solution is a pH regulator for the mixed solution.

9. A gold nanomaterial with regularly shaped etched depressions prepared by any of the methods of claims 1-8, characterized in that, The prepared gold nanomaterial is any one of a gold nanohexagonal plate, a gold nanotriangular plate, a gold nanocircular plate and a gold nanodecahedron.

10. A gold nanomaterial with regularly shaped etched depressions prepared by any of the methods according to claims 1-8, characterized in that: The prepared gold nanomaterial is a gold nanohexagonal plate, and its morphology is a hexagonal plate. There is an etched depression of regular shape on its (111) crystal plane, and the etched depression is mostly triangular, and the etched area can be adjusted with the reaction time.

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