A method for preparing silver nanosheets of adjustable size

Abstract

The application discloses a preparation method of silver nanosheets with adjustable size. The method uses silver nitrate etching seeds to control the product morphology. Specifically, silver nitrate is used to oxidize the seeds, so that more {111} crystal faces of the seeds are exposed. Meanwhile, a suitable gemini surfactant is used as a coating agent to tightly coat the {111} crystal faces, so that the seeds grow along the parallel direction of the {111} crystal faces, thereby obtaining silver nanosheets with adjustable size in a wide range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nano-silver material, in particular to a preparation method of silver nanosheet with adjustable size. BACKGROUND

[0002] Silver nanosheet has unique optical and electrical properties due to its sharp apex. The aspect ratio is usually used as an index to measure the anisotropy of silver nanosheet. The aspect ratio of nanosheet refers to the value of its side length divided by the thickness. In particular, when the nanosheet is large enough and thin enough, that is, it has a large enough aspect ratio, it not only shows dipole plasmon resonance, but also shows quadrupole plasmon resonance, and has multiple absorption peaks in the ultraviolet-visible region. Structure determines performance, and silver nanosheet has wide application value in the fields of sterilization, solar cells, organic light-emitting diodes, medical imaging, optical limiters, conductive ink, antibacterial, catalysis and the like.

[0003] In order to synthesize silver nanowire sheet, the crystal structure of silver nanosheet needs to be determined first. The characterization results show that the upper and lower main crystal faces of silver nanosheet are {111} crystal faces. Therefore, the key to synthesizing silver nanosheet is to control the crystal growth direction so as to grow along the direction parallel to the {111} crystal face.

[0004] Different reagents have a significant influence on the size and morphology of silver nanomaterials. The type of surfactant directly affects the final morphology of the nanostructure. Surfactant molecules tend to gather together in an aqueous solution with the polar group facing the water phase and the non-polar group away from the water phase. The aggregation behavior of surfactants in solution is affected by their own molecular structure, and the gemini surfactant has two hydrophobic tail chains, so it is more hydrophobic than single-chain surfactants. When the linking chain distance is short, the distance between the head groups in the molecule is greatly reduced. These factors enable gemini surfactants to form a more compact adsorption layer at the gas-liquid interface, making them more efficient and effective in reducing water surface tension. And due to the high variability of the molecular structure of gemini surfactants, they can form a variety of aggregate morphologies in aqueous solution, such as spherical micelles, ellipsoidal micelles, rod-shaped micelles, disc-shaped micelles, linear micelles, vesicles, lamellar phase, liquid crystal, sponge phase, etc. Different aggregate morphologies may have a certain influence on the shape and size of silver nanostructures. Therefore, gemini surfactants have excellent performance and are significantly superior to single-chain surfactants in most performance, and can be designed according to the needs to achieve the effect of controlling the structure of nanomaterials. SUMMARY

[0005] The present application aims to provide a preparation method of silver nanosheet with adjustable size, which is simple to operate and the whole process is carried out at normal pressure. By using suitable gemini surfactants, silver nanosheets with size controlled in a wide range can be prepared.

[0006] To achieve the above objectives, the solution of the present invention is:

[0007] A method for preparing size-tunable silver nanosheets includes the following steps:

[0008] Step 1, Preparation of seed crystals:

[0009] First, add 1 mL of 5%~50% (w / v) AgNO3 aqueous solution to 9 mL of 0.5%~10% (w / v) Gemini surfactant aqueous solution under stirring. Then, add 2 mL of 5%~50% (w / v) freshly prepared NaBH4 aqueous solution under vigorous stirring. After standing for 2~4 h, seed crystal A is obtained.

[0010] Step 2, Etching of the seed crystal:

[0011] Then, 0.2-2 mL of seed crystal A was added to 9 mL of an aqueous solution of 0.5%-10% (w / v) Gemini surfactant, followed by 1 mL of an aqueous solution of 10%-50% (w / v) AgNO3. The temperature was raised to 40-70℃ and kept at that temperature for 0.5-4 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0012] Step 3, One-step growth of the seed crystal:

[0013] After the obtained seed crystal B is cooled to room temperature, concentrated ammonia is added to adjust the pH value to 8-11. Then, 10 mL of 1%-10% (w / v) ascorbic acid aqueous solution is added and stirred evenly. Finally, the reaction solution is allowed to stand at 25°C for 1-14 h to allow the reaction to proceed fully, and a dispersion of silver nanosheets is obtained. The average particle size of the silver nanosheets is controlled in the range of 100-2000 nm.

[0014] In steps 1 and 2, the gemini surfactant is a quaternary ammonium salt surfactant with the molecular formula [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ];

[0015] Wherein, when s=4, the Gemini surfactant is denoted as 16-4-16; when s=6, the Gemini surfactant is denoted as 16-6-16; and when s=10, the Gemini surfactant is denoted as 16-10-16.

[0016] Furthermore, it also includes step 4, the two-step growth of the seed crystal:

[0017] Add 0.2-2 mL of the silver nanosheet dispersion obtained in step 3 to 9 mL of an aqueous solution of 0.5%-10% (w / v) Gemini surfactant, then add 1 mL of an aqueous solution of 5%-50% (w / v) AgNO3, then add concentrated ammonia to adjust the pH to 8-11, then add 10 mL of an aqueous solution of 2%-10% (w / v) ascorbic acid and stir until homogeneous. Finally, let the reaction solution stand at 25°C for 1-14 h to allow the reaction to proceed fully, and obtain a dispersion of silver nanosheets. The average particle size of the silver nanosheets is controlled within the range of 2000-5000 nm.

[0018] In step 4, the gemini surfactant is a quaternary ammonium salt surfactant with the molecular formula: [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ];

[0019] Wherein, when s=4, the Gemini surfactant is denoted as 16-4-16; when s=6, the Gemini surfactant is denoted as 16-6-16; and when s=10, the Gemini surfactant is denoted as 16-10-16.

[0020] In step 4, the dispersion of silver nanosheets obtained from the reaction is centrifuged, washed, and finally dispersed in water for storage; or dried at 80~100℃ for 4~24 h to obtain a powdered solid.

[0021] In step 3, the concentration of the concentrated ammonia solution is 25%~28% (w / v).

[0022] In step 3, the dispersion of silver nanosheets obtained from the reaction is centrifuged, washed, and finally dispersed in water for storage; or dried at 80~100℃ for 4~24 h to obtain a powdered solid.

[0023] By adopting the above technical solution, the method for preparing silver nanosheets with adjustable size according to the present invention has the following advantages:

[0024] One method involves using quaternary ammonium salt surfactants as inducers to synthesize silver nanosheets of desired shapes and sizes. The molecular structure of the quaternary ammonium salt surfactant is shown in Formula I. The connecting chain in the middle can be adjusted as needed, which is one of the key factors enabling the formation of high-yield silver nanosheets in this invention. Since gemini surfactants can form abundant aggregate structures in water, different aggregate structures may have a certain influence on the shape and size of the silver nanostructures. Therefore, this invention successfully synthesized silver nanosheets of different sizes by changing the length of the connecting chain. In contrast, traditional single-chain surfactants such as CTAB can only form nanoparticles or low-yield nanosheets.

[0025] Secondly, the innovation lies in the preparation method. Customizing the size of silver nanosheets according to requirements is a highly challenging problem. This invention achieves this goal through the following method: Since silver nitrate corrodes the crystal faces on the sides of silver nanosheets much faster than on the crystal faces at the ends of nanorods, and because the former's crystal faces are non-{111} crystal faces while the latter's are {111} crystal faces, silver nitrate corrodes the {111} crystal faces more slowly. Inspired by this, this invention attempts to control the morphology of the product by using seed crystals etched by silver nitrate. Specifically, silver nitrate is used to oxidize the seed crystals, exposing more {111} crystal faces on the surface of the seed crystals. At the same time, an appropriate quaternary ammonium salt gemini surfactant is used as a coating agent to tightly coat the {111} crystal faces, allowing them to grow in a direction parallel to the {111} crystal faces. By adjusting the length of the intermediate linking chain of the gemini surfactant, the amount of seed crystals added, and the pH value, silver nanosheets with tunable size over a wide range are obtained. The preparation method is simple to operate, and the whole process is carried out under normal pressure, making it highly operable. Attached Figure Description

[0026] Figure 1 SEM image of the silver nanosheets prepared in Example 1;

[0027] Figure 2 SEM image of the silver nanosheets prepared in Example 2;

[0028] Figure 3 Here is a SEM image of the silver nanosheets prepared in Example 3;

[0029] Figure 4 Here is a SEM image of the silver nanosheets prepared in Example 4;

[0030] Figure 5 Here is a SEM image of the silver nanosheets prepared in Example 5;

[0031] Figure 6 SEM image of the silver nanosheets prepared in Example 6;

[0032] Figure 7 SEM image of the silver nanosheets prepared in Example 7;

[0033] Figure 8 SEM image of the silver nanosheets prepared in Example 8;

[0034] Figure 9 This is a SEM image of the silver nanosheets prepared in Example 9. Detailed Implementation

[0035] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0036] Example 1

[0037] A method for preparing size-tunable silver nanosheets includes the following steps:

[0038] Step 1, Preparation of seed crystals:

[0039] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 2% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0040] Step 2, Etching of the seed crystal:

[0041] Then, 0.2 mL of seed crystal A was added to 9 mL of 2% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 10%~50% (w / v) AgNO3 aqueous solution. The temperature was raised to 40℃ and kept at that temperature for 0.5 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0042] Step 3, One-step growth of the seed crystal:

[0043] After the obtained seed crystals B were cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 8. Then, 10 mL of 1% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. The reaction solution was then allowed to stand at 25°C for 1 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 200 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 1 As shown, the average particle size is between 800 and 1000 nm.

[0044] In steps 1 and 2, the molecular formula of the gemini surfactant 16-4-16 is [C 16 H 33 N+ (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0045] Example 2

[0046] A method for preparing size-tunable silver nanosheets includes the following steps:

[0047] Step 1, Preparation of seed crystals:

[0048] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 0.5% (w / v) Gemini surfactant 16-6-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 4 h, seed crystal A was obtained.

[0049] Step 2, Etching of the seed crystal:

[0050] Then, 0.5 mL of seed crystal A was added to 9 mL of 0.5% (w / v) Gemini surfactant 16-6-16 aqueous solution, followed by 1 mL of 10% (w / v) AgNO3 aqueous solution. The temperature was raised to 60℃ and kept at that temperature for 4 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0051] Step 3, One-step growth of the seed crystal:

[0052] After the obtained seed crystal B was cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 11. Then, 10 mL of 1% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. The reaction solution was then allowed to stand at 25°C for 4 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 200 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 2 As shown, the average particle size is between 500 and 1000 nm.

[0053] In steps 1 and 2, the molecular formula of the gemini surfactant 16-6-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=6.

[0054] Example 3

[0055] A method for preparing size-tunable silver nanosheets includes the following steps:

[0056] Step 1, Preparation of seed crystals:

[0057] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 2% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0058] Step 2, Etching of the seed crystal:

[0059] Then, 0.2 mL of seed crystal A was added to 9 mL of 4% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 10% (w / v) AgNO3 aqueous solution. The temperature was raised to 50℃ and kept at that temperature for 0.5 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0060] Step 3, One-step growth of the seed crystal:

[0061] After the obtained seed crystals B were cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 9. Then, 10 mL of 1% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. The reaction solution was then allowed to stand at 25°C for 14 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 200 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 3 As shown, the average particle size is between 1000 and 1800 nm.

[0062] In steps 1 and 2, the molecular formula of the gemini surfactant 16-4-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0063] Example 4

[0064] A method for preparing size-tunable silver nanosheets includes the following steps:

[0065] Step 1, Preparation of seed crystals:

[0066] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 3% (w / v) Gemini surfactant 16-10-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0067] Step 2, Etching of the seed crystal:

[0068] Then, 0.6 mL of seed crystal A was added to 9 mL of 2% (w / v) Gemini surfactant 16-10-16 aqueous solution, followed by 1 mL of 10% (w / v) AgNO3 aqueous solution. The temperature was raised to 60℃ and kept at that temperature for 2 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0069] Step 3, One-step growth of the seed crystal:

[0070] After the obtained seed crystals B were cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 8. Then, 10 mL of 2% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. The reaction solution was then allowed to stand at 25°C for 14 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 300 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 4 As shown, the average particle size is between 400 and 1000 nm.

[0071] In steps 1 and 2, the molecular formula of the gemini surfactant 16-10-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=10.

[0072] Example 5

[0073] A method for preparing size-tunable silver nanosheets includes the following steps:

[0074] Step 1, Preparation of seed crystals:

[0075] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 10% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0076] Step 2, Etching of the seed crystal:

[0077] Then, 1 mL of seed crystal A was added to 9 mL of 10% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 10% (w / v) AgNO3 aqueous solution. The temperature was raised to 40℃ and kept at that temperature for 4 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0078] Step 3, One-step growth of the seed crystal:

[0079] After the obtained seed crystal B was cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 10. Then, 10 mL of 2% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. Finally, the reaction solution was allowed to stand at 25°C for 14 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 200 r / min, washed with deionized water, and finally dried at 80°C for 12 h to obtain a powdered solid. The SEM image of the silver nanosheets is shown below. Figure 5 As shown, the average particle size is between 200 and 500 nm.

[0080] In steps 1 and 2, the molecular formula of the gemini surfactant 16-4-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0081] Example 6

[0082] A method for preparing size-tunable silver nanosheets includes the following steps:

[0083] Step 1, Preparation of seed crystals:

[0084] First, 1 mL of 10% (w / v) AgNO3 aqueous solution was added to 9 mL of 6% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 10% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0085] Step 2, Etching of the seed crystal:

[0086] Then, 2 mL of seed crystal A was added to 9 mL of 6% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 10% (w / v) AgNO3 aqueous solution. The temperature was raised to 70℃ and held for 0.5 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0087] Step 3, One-step growth of the seed crystal:

[0088] After the obtained seed crystal B was cooled to room temperature, 25% (w / v) concentrated ammonia was added to adjust the pH to 10. Then, 10 mL of 1% (w / v) ascorbic acid aqueous solution was added and stirred thoroughly. Finally, the reaction solution was allowed to stand at 25°C for 6 h to allow the reaction to proceed completely, resulting in a dispersion of silver nanosheets. The dispersion was centrifuged at 8000 r / min, washed with deionized water, and finally dried at 80°C for 4 h to obtain a powdered solid. The SEM image of the silver nanosheets is shown below. Figure 6 As shown, the average particle size is between 100 and 200 nm.

[0089] In steps 1 and 2, the molecular formula of the gemini surfactant 16-4-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0090] Example 7

[0091] A method for preparing size-tunable silver nanosheets includes the following steps:

[0092] Step 1, Preparation of seed crystals:

[0093] First, 1 mL of 20% (w / v) AgNO3 aqueous solution was added to 9 mL of 3% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 20% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0094] Step 2, Etching of the seed crystal:

[0095] Then, 2 mL of seed crystal A was added to 9 mL of 3% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 20% (w / v) AgNO3 aqueous solution. The temperature was raised to 40℃ and kept at that temperature for 4 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0096] Step 3, One-step growth of the seed crystal:

[0097] After the obtained seed crystal B is cooled to room temperature, 25% (w / v) concentrated ammonia is added to adjust the pH value to 11. Then, 10 mL of 2% (w / v) ascorbic acid aqueous solution is added and stirred evenly. Finally, the reaction solution is allowed to stand at 25°C for 14 h to allow the reaction to proceed fully, and a dispersion of silver nanosheets is obtained.

[0098] Step 4, Two-step growth of the seed crystal:

[0099] Two mL of the silver nanosheet dispersion obtained in step 3 was added to nine mL of a 3% (w / v) aqueous solution of Gemini surfactant 16-4-16. Then, one mL of a 20% (w / v) aqueous solution of AgNO3 was added, followed by the addition of 25% (w / v) concentrated ammonia to adjust the pH to 11. Next, 10 mL of a 2% (w / v) aqueous solution of ascorbic acid was added and stirred until homogeneous. The reaction solution was then allowed to stand at 25 °C for 14 h to allow the reaction to proceed fully, resulting in another silver nanosheet dispersion. This dispersion was centrifuged at 200 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 7 As shown, the average particle size is 2000 nm.

[0100] In steps 1, 2, and 4, the molecular structural formula of the gemini surfactant 16-4-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0101] Example 8

[0102] A method for preparing size-tunable silver nanosheets includes the following steps:

[0103] Step 1, Preparation of seed crystals:

[0104] First, 1 mL of 20% (w / v) AgNO3 aqueous solution was added to 9 mL of 4% (w / v) Gemini surfactant 16-4-16 aqueous solution under stirring. Then, 2 mL of 20% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0105] Step 2, Etching of the seed crystal:

[0106] Then, 1 mL of seed crystal A was added to 9 mL of 4% (w / v) Gemini surfactant 16-4-16 aqueous solution, followed by 1 mL of 20% (w / v) AgNO3 aqueous solution. The temperature was raised to 40℃ and kept at that temperature for 0.5 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0107] Step 3, One-step growth of the seed crystal:

[0108] After the obtained seed crystal B is cooled to room temperature, 25% (w / v) concentrated ammonia is added to adjust the pH value to 11. Then, 10 mL of 2% (w / v) ascorbic acid aqueous solution is added and stirred evenly. Finally, the reaction solution is allowed to stand at 25°C for 14 h to allow the reaction to proceed fully, and a dispersion of silver nanosheets is obtained.

[0109] Step 4, Two-step growth of the seed crystal:

[0110] 1 mL of the silver nanosheet dispersion obtained in step 3 was added to 9 mL of a 4% (w / v) aqueous solution of Gemini surfactant 16-4-16, followed by 1 mL of a 20% (w / v) aqueous solution of AgNO3. Then, 25% (w / v) concentrated ammonia was added to adjust the pH to 11. Next, 10 mL of a 2% (w / v) aqueous solution of ascorbic acid was added and stirred until homogeneous. The reaction solution was then allowed to stand at 25 °C for 14 h to allow the reaction to proceed fully, resulting in another silver nanosheet dispersion. This dispersion was centrifuged at 200 r / min, washed with deionized water, and finally stored in water. The SEM image of the silver nanosheets is shown below. Figure 8 As shown, the average particle size is 3000 nm.

[0111] In steps 1, 2, and 4, the molecular formula of the gemini surfactant 16-4-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=4.

[0112] Example 9

[0113] A method for preparing size-tunable silver nanosheets includes the following steps:

[0114] Step 1, Preparation of seed crystals:

[0115] First, 1 mL of 20% (w / v) AgNO3 aqueous solution was added to 9 mL of 3% (w / v) Gemini surfactant 16-10-16 aqueous solution under stirring. Then, 2 mL of 20% (w / v) freshly prepared NaBH4 aqueous solution was added under vigorous stirring. After standing for 2 h, seed crystal A was obtained.

[0116] Step 2, Etching of the seed crystal:

[0117] Then, 0.5 mL of seed crystal A was added to 9 mL of 5% (w / v) Gemini surfactant 16-10-16 aqueous solution, followed by 1 mL of 20% (w / v) AgNO3 aqueous solution. The temperature was raised to 70℃ and kept at that temperature for 0.5 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B.

[0118] Step 3, One-step growth of the seed crystal:

[0119] After the obtained seed crystal B is cooled to room temperature, 25% (w / v) concentrated ammonia is added to adjust the pH value to 11. Then, 10 mL of 2% (w / v) ascorbic acid aqueous solution is added and stirred evenly. Finally, the reaction solution is allowed to stand at 25°C for 14 h to allow the reaction to proceed fully, and a dispersion of silver nanosheets is obtained.

[0120] Step 4, Two-step growth of the seed crystal:

[0121] 0.5 mL of the silver nanosheet dispersion obtained in step 3 was added to 9 mL of a 3% (w / v) aqueous solution of Gemini surfactant 16-10-16, followed by 1 mL of a 20% (w / v) aqueous solution of AgNO3. Then, 25% (w / v) concentrated ammonia was added to adjust the pH to 11. Next, 10 mL of a 2% (w / v) aqueous solution of ascorbic acid was added and stirred until homogeneous. The reaction solution was then allowed to stand at 25°C for 14 h to allow the reaction to proceed fully, resulting in a silver nanosheet dispersion. This dispersion was centrifuged at 200 r / min, washed with deionized water, and finally dried at 80°C for 24 h to obtain a powdered solid. The SEM image of the silver nanosheets is shown below. Figure 9 As shown, the average particle size is between 3000 and 5000 nm.

[0122] In steps 1, 2, and 4, the molecular formula of the gemini surfactant 16-10-16 is [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ], where s=10.

[0123] In this invention, the operations such as "vigorous stirring", "stirring", "centrifugation" and "washing" are conventional operations in the field. Those skilled in the art should know that the degree of stirring in "vigorous stirring" is greater than that in "stirring".

[0124] In this invention, the method for synthesizing quaternary ammonium salt surfactants is a well-known method in the art. Zana reported the synthesis of quaternary ammonium salt surfactants in 1991 (Zana R, Benrraou M, Rueff R. Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants. 1. Effect of the spacer chain length on the critical micelle concentration and micelleionization degree[J]. Langmuir , 1991, 7(6): 1072-1075), the reaction equation is as shown in equation I.

[0125] N(CH3)2C m H 2m+1 + Br (CH2) n Br → [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ]

[0126] Formula I

[0127] Referring to the above synthesis method, the synthesis method of the gemini surfactant 16-10-16 is illustrated as follows: 24.8 g (92.2 mmol) N , N Dimethylhexadecanine was added to a 250 mL round-bottom flask, followed by 100 mL of ethyl acetate as a solvent. Then, 12.5 g (41.7 mmol) of 1,10-dibromodecane was added, and the mixture was refluxed with stirring for 48 hours. After cooling to room temperature, a white precipitate was formed. The precipitate was collected by filtration, and the resulting solid was redissolved in a mixed solvent of ethyl acetate and ethanol and recrystallized five times. Finally, a trace amount of solvent was removed by pumping out the solid, yielding a white powdery solid, which is the Gemini surfactant 16-10-16. The reaction equation is shown in Formula II.

[0128] N(CH3)2C 16 H 33 + Br (CH2) 10 Br → [C 16 H 33 N + (CH3)2(CH2) 10 (CH3)2N + C 16 H 33 ][2 Br - ]

[0129] Formula II

[0130] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A method for preparing size-tunable silver nanosheets, characterized in that: Includes the following steps: Step 1, Preparation of seed crystals: First, add 1 mL of 5%~50% (w / v) AgNO3 aqueous solution to 9 mL of 0.5%~10% (w / v) Gemini surfactant aqueous solution under stirring. Then, add 2 mL of 5%~50% (w / v) freshly prepared NaBH4 aqueous solution under vigorous stirring. After standing for 2~4 h, seed crystal A is obtained. Step 2, Etching of the seed crystal: Then, 0.2-2 mL of seed crystal A was added to 9 mL of an aqueous solution of 0.5%-10% (w / v) Gemini surfactant, followed by 1 mL of an aqueous solution of 10%-50% (w / v) AgNO3. The temperature was raised to 40-70℃ and kept at that temperature for 0.5-4 h to complete the etching of the seed crystal. The resulting product was denoted as seed crystal B. Step 3, One-step growth of the seed crystal: After the obtained seed crystal B is cooled to room temperature, concentrated ammonia is added to adjust the pH value to 8-11. Then, 10 mL of 1%-10% (w / v) ascorbic acid aqueous solution is added and stirred evenly. Finally, the reaction solution is allowed to stand at 25°C for 1-14 h to allow the reaction to proceed fully, and a dispersion of silver nanosheets is obtained. The average particle size of the silver nanosheets is controlled in the range of 100-2000 nm. In steps 1 and 2, the gemini surfactant is a quaternary ammonium salt surfactant with the molecular formula [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ]; Wherein, when s=4, the Gemini surfactant is denoted as 16-4-16; when s=6, the Gemini surfactant is denoted as 16-6-16; and when s=10, the Gemini surfactant is denoted as 16-10-16.

2. The method for preparing size-tunable silver nanosheets according to claim 1, characterized in that: It also includes step 4, the two-step growth of the seed crystal: Add 0.2-2 mL of the silver nanosheet dispersion obtained in step 3 to 9 mL of an aqueous solution of 0.5%-10% (w / v) Gemini surfactant, then add 1 mL of an aqueous solution of 5%-50% (w / v) AgNO3, then add concentrated ammonia to adjust the pH to 8-11, then add 10 mL of an aqueous solution of 2%-10% (w / v) ascorbic acid and stir until homogeneous. Finally, let the reaction solution stand at 25 °C for 1-14 h to allow the reaction to proceed fully, and obtain a dispersion of silver nanosheets, wherein the average particle size of the silver nanosheets is controlled in the range of 2000-5000 nm.

3. The method for preparing size-tunable silver nanosheets according to claim 2, characterized in that: In step 4, the gemini surfactant is a quaternary ammonium salt surfactant with the molecular formula [C 16 H 33 N + (CH3)2(CH2) s (CH3)2N + C 16 H 33 ][2 Br - ]; Wherein, when s=4, the Gemini surfactant is denoted as 16-4-16; when s=6, the Gemini surfactant is denoted as 16-6-16; and when s=10, the Gemini surfactant is denoted as 16-10-16.

4. The method for preparing size-tunable silver nanosheets according to claim 2, characterized in that: In step 4, the dispersion of silver nanosheets obtained from the reaction is centrifuged, washed, and finally dispersed in water for storage; or dried at 80~100℃ for 4~24 h to obtain a powdered solid.

5. The method for preparing size-tunable silver nanosheets according to claim 1, characterized in that: In step 3, the concentration of the concentrated ammonia solution is 25%~28% (w / v).

6. The method for preparing size-tunable silver nanosheets according to claim 1, characterized in that: In step 3, the dispersion of silver nanosheets obtained from the reaction is centrifuged, washed, and finally dispersed in water for storage; or dried at 80~100℃ for 4~24 h to obtain a powdered solid.

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