Preparation of quasi-two-dimensional nanoscale sawtooth on gold substrate by selective chemical etching of thiol ligand and method thereof

Abstract

The present invention relates to a method for preparing quasi-two-dimensional nanoscale sawtooth using gold nano triangular sheets or hexagonal sheets as substrates. The method preferentially protects the tip position with higher curvature on the surface of the gold nanosheet by utilizing the curvature-specific affinity of the thiol ligand (2-naphthol), and chemically etches the tip position to be more and more pointed, and the flat position to be more and more deeply engraved, and finally forms continuous and uniform nanoscale sawtooth. It can be used as a new type of functional complex nanomaterial, and its unique nanoscale sawtooth structure has the potential to become a future micro-nano tool. The method is simple to operate and has strong universality, subverts the etching rules that usually make nanostructures more and more smooth, and provides a new method for the synthesis of new nanomaterials.

Description

Technical Field

[0001] The present invention relates to the field of functional inorganic nanomaterial preparation, in particular to the preparation of complex nanostructures by reprocessing precious metal nanomaterials. Background Art

[0002] When the size of materials is reduced to the nanoscale, the same components will have completely new properties due to the dramatic change in size. The emergence and rise of precious metal nanomaterials have set off tremendous changes in the fields of electronic devices, medicine and health, aerospace, aviation and space exploration, environment, resources and energy, biotechnology, etc. Compared with traditional materials, the laying of nano-scale precious metals makes devices smaller and more portable; their stronger optical, thermal, magnetic and electrical properties give the materials stronger efficiency, and their stronger mechanical properties give the materials sufficient strength and toughness. As the first of the precious metals, gold nanoparticles have excellent plasmonic resonance effects (plasmonic), electromagnetic coupling and photothermal effects. Therefore, the design and preparation of nano-gold materials is currently a hot topic.

[0003] More exotic and complex nanomaterials often have higher surface energy and more active sites than primary nanomaterials due to their unique shapes, so they are expected to become the next generation of functional nanomaterials. Sawtooth is a powerful tool in daily life. It makes it easy to cut objects. It can be imagined that the characteristics of sawtooth are equally applicable to the cutting of macroscopic objects and the destruction of chemical bonds. However, in the growth and etching of nanoparticles, due to thermodynamic reasons, they often grow and carve in a rounder and smoother direction. It is difficult to shape orderly sawtooth on a flat surface, although the existing nanosynthesis technology can synthesize sufficiently sharp spikes and nanoparticles with abundant spikes. However, these spikes do not have a cutting surface formed by flatness in one dimension like sawtooth. There is a huge difference between the two. Even if these randomly distributed spikes are neatly arranged, the function of sawtooth cannot be realized. Therefore, the method of shaping regular and continuously distributed sawtooth is still missing.

[0004] In view of the above reasons, it is crucial to subvert the design and scheme of the usual etching mode and prepare quasi-two-dimensional nanoscale sawtooth on the gold substrate. Summary of the invention

[0005] The technical problem solved by the invention is: a method for selective chemical etching using thiol ligands is proposed, and the tip of the substrate material is protected by the curvature-specific affinity of the thiol molecules, and finally a quasi-two-dimensional nano-scale sawtooth on a gold substrate is prepared.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is: a method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching of thiol ligands, characterized in that: the specific steps are as follows:

[0007] Step (1): centrifugally purify the gold nanosheets and disperse them in a mixed solution of 2-naphthol, N,N-dimethylformamide and water; after dispersion, fully stir the mixture until it is uniform, and the total volume can be increased or decreased according to demand to obtain a colloidal system mixture;

[0008] Step (2): placing the colloidal system mixture prepared in step (1) in a 45°C-70°C oven or water bath for constant temperature incubation for 1-4 hours, and cooling to room temperature for later use after the incubation is completed;

[0009] Step (3): centrifuging the mixture of step (2) and removing the supernatant, re-dispersing it with a hexadecyltrimethylammonium bromide (CTAB) aqueous solution, centrifuging it again to remove the supernatant, and repeating this operation twice to completely remove the free thiol molecules;

[0010] Step (4): Re-disperse the gold nanosheets washed in step (3) into a CTAB aqueous solution, add a chloroauric acid aqueous solution (adjusted according to the total volume) thereto to start etching, and let the system stand for 1-3 hours;

[0011] Step (5): After the reaction is completed, the system is subjected to multiple centrifugal purifications to remove the remaining chloroauric acid, thereby obtaining a quasi-two-dimensional nanoscale sawtooth on a gold substrate, which can be dispersed with a CTAB solution for stable storage.

[0012] Preferably, in step (1), the centrifugal speed of the gold nanosheets is 4000 rcf, and the centrifugal time is 10 min; after two centrifugal purifications, the volume ratio of the dispersed DMF and water mixed solution is 1:4, and the molar concentration of 2-naphthol in the mixture is 0.1-10 mM.

[0013] Preferably, the mixture is heated at a temperature of 60° C. in step (2).

[0014] Preferably, in step (3), the first centrifugation speed is 4500 rcf, the time is 10 min, the mass fraction of CTAB used in the washing process is 98%, the concentration is 5 mM, and the second centrifugation speed is 3600 rcf, the time is 10 min.

[0015] Preferably, in step (4), the concentration of CTAB is 0.1 M, the chloroauric acid is tetrachloroauric acid trihydrate, the concentration is 2 mg / mL, the added volume is 5 μL-500 μL, and the reaction time is 0.5 h-3 h.

[0016] Preferably, in step (5), the centrifugal speed is 3800 rcf for 10 min, the second centrifugal speed is 3300 rcf for 10 min, and the CTAB concentration is 0.05 M.

[0017] Preferably, the method comprises the following steps:

[0018] (1) Incubation of gold nanosheets with thiol ligands: Take any volume of gold nanosheets, centrifuge at 4000 rcf for 10 min, remove the supernatant, and repeat centrifugation to completely remove the surface ligands; disperse the gold nanosheets with a DMF and water mixed solution with a concentration of 0.1-10 mM 2-naphthol (DMF: water volume ratio is 1:4), and then place the mixture in a 60°C oven or water bath for 2 h. After the incubation is completed, cool it to room temperature for further use;

[0019] (2) Washing away excess thiol ligands: Centrifuge the mixture in step (1) at 4500 rcf for 10 min to remove the supernatant, prepare an equal volume of 5 mM CTAB aqueous solution to the mixture and disperse it again, centrifuge it at 3800 rcf for 10 min, remove the supernatant, repeat this step twice, the second centrifugation speed is 3300 rcf, and the time is 10 min;

[0020] (3) Etching of gold nanosheets: Prepare a 0.1M CTAB aqueous solution of the same volume as in step (1) to disperse the gold nanosheets washed in step (2), then add a 2mg / ml chloroauric acid aqueous solution thereto in a volume of 5μL-500μL. If the amount to be added is large, it can be added in multiple times. After fully mixing, let the reaction stand for 0.5-3h, and then centrifuge and wash to obtain the final product.

[0021] In order to solve the above technical problems, the present invention proposes another technical solution: quasi-two-dimensional nanoscale sawtooth on a gold substrate prepared by any of the above methods.

[0022] Beneficial effects of the present invention:

[0023] (1) This method is simple and universal. The substrate material is not only applicable to gold nanotriangular flakes, but also to all gold flakes of different sizes and types. Selecting different substrates can shape sawtooth structures of various styles and sizes.

[0024] (2) This method can obtain nanoscale sawtooth and can precisely adjust the number and size of sawtooth by adjusting multiple factors such as 2-naphthol and etching time.

[0025] (3) This material can be widely used in quantitative analysis and trace detection.

[0026] (4) The unique sawtooth shape of the invention has great application potential in chemical analysis, sensors, photocatalysis, biomedicine, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1(a) Transmission electron microscopy (TEM) image of the quasi-two-dimensional nanoscale sawtooth structure of the gold substrate obtained after etching (b) UV-Vis-CRT images obtained before and after etching

[0029] Infrared absorption spectrum

[0030] Figure 2 This is the TEM image of the gold sheet with a lower number of sawtooth produced when the etching time is 1 hour.

[0031] Figure 3 TEM images of saw teeth with different numbers of teeth etched at different 2-naphthol concentrations (a) 10mM (b) 1mM (c) 0.1mM

[0032] Figure 4 It uses a larger hexagonal sheet as the base material for sawtooth etching.

[0033] Figure 5 This is a comparison of the Raman spectra of the gold sheet before and after etching to form sawtooth

[0034] Figure 6 This is the TEM image of the etching after the 2-naphthol was completely removed.

[0035] Figure 7 TEM image of the etching result after replacing 2-naphthol with n-dodecyl mercaptan DETAILED DESCRIPTION

[0036] Example 1

[0037] (1) Synthesis method of gold nanotriangular flakes: Seed synthesis: 0.5 ml of 20 mM chloroauric acid aqueous solution and 1 ml of 10 mM trisodium citrate aqueous solution were added to 36.5 ml of ultrapure water. Then, 1 ml of 0.1 M sodium borohydride aqueous solution was added under vigorous stirring, and the mixture was stirred for 2 min and allowed to stand for 4 h for use.

[0038] Preparation of growth solution: Prepare 108ml of 0.025M CTAB aqueous solution, then add 1.5ml of 0.02M chloroauric acid aqueous solution, 0.6ml of 0.1M sodium hydroxide aqueous solution, 54μL of 0.1M potassium iodide aqueous solution, and 0.6ml of 0.1M L-ascorbic acid in sequence; stir the mixture thoroughly. Then divide the growth solution into 0.9ml, 9ml, and 92ml, add 100μL of seeds to 0.9ml of growth solution, shake gently for 3s, and then pour it all into 9ml of growth solution, shake gently for 3s again, and then pour it all into 92ml of growth solution again, shake thoroughly and evenly, and then let it stand at room temperature overnight. All the products are deposited at the bottom of the bottle.

[0039] (2) Incubate gold nanosheets with thiol ligands. Take 500 μL of gold nanosheets, centrifuge at 4000 rcf for 10 min, remove the supernatant, and repeat centrifugation and washing to completely remove the surface ligands. Disperse the gold nanosheets with a DMF and water mixed solution (volume ratio of 1:4) with a 2-naphthol concentration of 4 mM, and then place the mixture in a 60°C oven or water bath for 2 h. After incubation, cool it to room temperature for further use.

[0040] (3) Wash away excess thiol ligands. Centrifuge the mixture in (1) at 4500 rcf for 10 min to remove the supernatant, prepare an equal volume of 5 mM CTAB aqueous solution to the mixture and disperse again, centrifuge again at 3800 rcf for 10 min, and remove the supernatant. Repeat this step twice, the second centrifugation speed is 3300 rcf, and the time is 10 min.

[0041] (4) Etching of gold nanosheets. Prepare a 0.1M CTAB aqueous solution of the same volume as (1) to disperse the gold nanosheets washed in step (2), then add a 2mg / ml chloroauric acid aqueous solution to it, the added volume is 10μL, and when the added amount is large, it can be added in multiple times, and after fully mixing, let it stand for 3 hours to react. After centrifugation and washing, the final product is obtained.

[0042] (5) Figure 1 b UV-visible-near infrared spectra before and after etching, where 1, 2, 3, and 4 refer to the addition of chloroauric acid in volumes of 5 μL, 10 μL, 15 μL, and 20 μL, respectively.

[0043] It can be clearly seen that the absorption peaks of the gold nanotriangles at 832nm and 1300nm have a certain degree of blue shift, and the absorption peak at 785nm gradually increases with the increase of etching degree. It is predicted that there will be strong surface enhanced Raman scattering (SERS) under laser excitation at this wavelength.

[0044] Example 2

[0045] (1) Synthesis method of gold nanotriangular flakes: Seed synthesis: 0.5 ml of 20 mM chloroauric acid aqueous solution and 1 ml of 10 mM trisodium citrate aqueous solution were added to 36.5 ml of ultrapure water. Then, 1 ml of 0.1 M sodium borohydride aqueous solution was added under vigorous stirring, and the mixture was stirred for 2 min and allowed to stand for 4 h for use.

[0046] Preparation of growth solution: Prepare 108ml of 0.025M CTAB aqueous solution, then add 1.5ml of 0.02M chloroauric acid aqueous solution, 0.6ml of 0.1M sodium hydroxide aqueous solution, 54μL of 0.1M potassium iodide aqueous solution, and 0.6ml of 0.1M L-ascorbic acid in sequence; stir the mixture thoroughly. Then divide the growth solution into 0.9ml, 9ml, and 92ml, add 100μL of seeds to 0.9ml of growth solution, shake gently for 3s, and then pour it all into 9ml of growth solution, shake gently for 3s again, and then pour it all into 92ml of growth solution again, shake thoroughly and evenly, and then let it stand at room temperature overnight. All the products are deposited at the bottom of the bottle.

[0047] (2) Incubate gold nanosheets with thiol ligands. Take 500 μL of gold nanosheets, centrifuge at 4000 rcf for 10 min, remove the supernatant, and repeat centrifugation and washing to completely remove the surface ligands. Disperse the gold nanosheets with a DMF and water mixed solution (volume ratio of 1:4) with a 2-naphthol concentration of 0.1 mM, and then place the mixture in a 45°C oven or water bath for 2 h. After incubation, cool it to room temperature for further use.

[0048] (3) Wash away excess thiol ligands. Centrifuge the mixture in (1) at 4500 rcf for 10 min to remove the supernatant, prepare an equal volume of 5 mM CTAB aqueous solution to the mixture and disperse again, centrifuge again at 3800 rcf for 10 min, and remove the supernatant. Repeat this step twice, the second centrifugation speed is 3300 rcf, and the time is 10 min.

[0049] (4) Etching of gold nanosheets. Prepare a 0.1M CTAB aqueous solution of the same volume as (1) to disperse the gold nanosheets washed in step (2), then add a 2mg / ml chloroauric acid aqueous solution to it, the added volume is 10μL, and when the added amount is large, it can be added in multiple times, and after fully mixing, let it stand for 3 hours to react. After centrifugation and washing, the final product is obtained.

[0050] Example 3

[0051] (1) Synthesis method of gold nanotriangular flakes: Seed synthesis: 0.5 ml of 20 mM chloroauric acid aqueous solution and 1 ml of 10 mM trisodium citrate aqueous solution were added to 36.5 ml of ultrapure water. Then, 1 ml of 0.1 M sodium borohydride aqueous solution was added under vigorous stirring, and the mixture was stirred for 2 min and allowed to stand for 4 h for use.

[0052] Preparation of growth solution: Prepare 108ml of 0.025M CTAB aqueous solution, then add 1.5ml of 0.02M chloroauric acid aqueous solution, 0.6ml of 0.1M sodium hydroxide aqueous solution, 54μL of 0.1M potassium iodide aqueous solution, and 0.6ml of 0.1M L-ascorbic acid in sequence; stir the mixture thoroughly. Then divide the growth solution into 0.9ml, 9ml, and 92ml, add 100μL of seeds to 0.9ml of growth solution, shake gently for 3s, and then pour it all into 9ml of growth solution, shake gently for 3s again, and then pour it all into 92ml of growth solution again, shake thoroughly and evenly, and then let it stand at room temperature overnight. All the products are deposited at the bottom of the bottle.

[0053] (2) Incubate gold nanosheets with thiol ligands. Take 5000 μL of gold nanosheets, centrifuge at 4000 rcf for 10 min, remove the supernatant, and repeat centrifugation to completely remove the surface ligands. Disperse the gold nanosheets with a DMF and water mixture solution (volume ratio of 1:4) with a 2-naphthol concentration of 10 mM, and then place the mixture in a 70°C oven or water bath for 2 h. After incubation, cool it to room temperature for further use.

[0054] (3) Wash away excess thiol ligands. Centrifuge the mixture in (1) at 4500 rcf for 10 min to remove the supernatant, prepare an equal volume of 5 mM CTAB aqueous solution to the mixture and disperse again, centrifuge again at 3800 rcf for 10 min, and remove the supernatant. Repeat this step twice, the second centrifugation speed is 3300 rcf, and the time is 10 min.

[0055] (4) Etching of gold nanosheets. Prepare a 0.1M CTAB aqueous solution of the same volume as (1) to disperse the gold nanosheets washed in step (2), then add a 2mg / ml chloroauric acid aqueous solution to it, the added volume is 100μL, add it several times, mix it thoroughly and let it stand for 3h. After centrifugation and washing, the final product is obtained.

[0056] Example 4

[0057] Compared with Example 1, the etching time in step (4) is changed to 1 h. Figure 2 Finally, the product etching degree was significantly lower than that of the sample etched for 3h, and the average number of sawtooth was significantly higher than that of the sample etched for 3h.

[0058] Example 5

[0059] Adjust the concentration of 2-naphthol during the thiol ligand incubation step. Figure 3 The concentrations of a, b, and c are 10mM, 1mM, and 0.1mM, respectively. It can be clearly seen that the average number of sawtooth decreases sharply with the decrease of ligand concentration. The number of sawtooth of a single gold sheet can be directly controlled by adjusting the ligand concentration.

[0060] Example 6

[0061] The substrate material was replaced from triangular sheets to larger hexagonal sheets of gold, and other conditions were kept unchanged. After etching for 3 hours, the jagged TEM image of the hexagonal sheet of gold was obtained, as shown in Figure 2. Figure 4 As shown, sharp serrated structures are also formed at the edges of the gold hexagonal sheets, which proves the universality of this method.

[0062] Example 7

[0063] We characterized and compared the Raman spectra of the gold triangles incubated with 4 mM 2-naphthol and the gold triangles etched after incubation at the same ligand concentration. Figure 5 ,We found that the Raman signal intensity of the sawtooth structure formed after etching was significantly stronger than that of the unetched sample, which confirms the potential of sawtooth materials in quantitative analysis and trace detection.

[0064] Comparative Example 1

[0065] When no thiol ligand is introduced at all under the incubation conditions, other conditions remain unchanged, such as Figure 6 The results after etching show that all the golden triangles have turned into round pieces, the tip parts have been etched away, and no sawtooth structure appears.

[0066] Comparative Example 2

[0067] The ligand 2-naphthol used in the incubation was replaced with n-dodecyl mercaptan, and the other steps were the same as those in Example 1, such as Figure 7 As shown, the gold flakes are fused together due to the action of the etchant and no zigzag structure is formed, which illustrates the key role of the 2-naphthol ligand we used.

[0068] The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching of thiol ligands, characterized in that: The specific steps are as follows: Step (1): Incubate the gold nanosheets with thiol ligands: Take any volume of gold nanosheets, centrifuge at 4000 rcf for 10 min, remove the supernatant, and repeat centrifugation to completely remove the surface ligands; disperse the gold nanosheets with a DMF and water mixed solution with a concentration of 0.1-10mM 2-naphthol, and a DMF:water volume ratio of 1:4, and then place the mixture in a 60°C oven or water bath for 2 h. After the incubation is completed, cool it to room temperature for further use; Step (2): After centrifugation and purification, the gold nanosheets are dispersed in a mixed solution of 2-naphthol, N,N-dimethylformamide and water; after dispersion, the mixture is fully stirred until uniform to obtain a colloidal system mixture; Step (3): Wash away excess thiol ligands: Centrifuge the mixture in step (2) at 4500 rcf for 10 min, remove the supernatant, prepare an equal volume of 5 mM CTAB aqueous solution to disperse the mixture again, centrifuge again at 3800 rcf for 10 min, remove the supernatant, repeat this step twice, the second centrifugation speed is 3300 rcf, and the time is 10 min; Step (4): Etching of gold nanosheets: Prepare a 0.1 M CTAB aqueous solution of the same volume as in step (1) to disperse the gold nanosheets washed in step (3), then add a 2 mg / ml chloroauric acid aqueous solution in a volume of 5 μL-500 μL. If the amount is large, add it in multiple times. After fully mixing, let it stand for reaction for 0.5-3 h, and centrifuge and wash to obtain the final product; Step (5): placing the colloidal system mixture prepared in step (4) in a 45°C-70°C oven or water bath for constant temperature incubation for 1-4 hours, and cooling to room temperature for later use after the incubation is completed; Step (6): centrifuging the mixture of step (5) and removing the supernatant, re-dispersing it with a hexadecyltrimethylammonium bromide (CTAB) aqueous solution, centrifuging it again and removing the supernatant, and repeating this operation twice to completely remove the free thiol molecules; Step (7): Re-disperse the gold nanosheets washed in step (6) into a CTAB aqueous solution, add a chloroauric acid aqueous solution thereto to initiate etching, and allow the colloidal system mixture to stand for 1-3 h; Step (8): After the reaction is completed, the colloidal system mixture is subjected to multiple centrifugal purifications to remove the remaining chloroauric acid, thereby obtaining a quasi-two-dimensional nanoscale sawtooth on a gold substrate, which can be dispersed in a CTAB solution for stable storage.

2. The method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to claim 1, characterized in that: In step (1), the centrifugal speed of the gold nanosheets is 4000 rcf, and the centrifugal time is 10 min. After two centrifugal purifications, the volume ratio of the dispersed DMF and water mixed solution is 1:4, and the molar concentration of 2-naphthol in the mixture is 0.1-10mM.

3. The method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to claim 1, characterized in that: The mixture is heated to 60°C in step (2).

4. The method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to claim 1, characterized in that: In step (3), the first centrifugation speed is 4500 rcf and the time is 10 min. The mass fraction of CTAB used in the washing process is 98% and the concentration is 5 mM. The second centrifugation speed is 3600 rcf and the time is 10 min.

5. The method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to claim 1, characterized in that: In step (4), the concentration of CTAB is 0.1 M, the chloroauric acid is tetrachloroauric acid trihydrate, the concentration is 2 mg / mL, the added volume is 5 μL-500 μL, and the reaction time is 0.5 h-3 h.

6. The method for preparing quasi-two-dimensional nanoscale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to claim 1, characterized in that: In step (5), the centrifugation speed is 3800 rcf for 10 min, and the second centrifugation speed is 3300 rcf for 10 min; the concentration of CTAB is 0.05 M.

7. Quasi-two-dimensional nano-scale sawtooth on a gold substrate prepared by the method for preparing quasi-two-dimensional nano-scale sawtooth on a gold substrate by selective chemical etching with thiol ligands according to any one of claims 1 to 6.

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