A Preparation Method of Five-Fold Twinned Decahedral Au NCs

Abstract

The present invention discloses a preparation method of quintuple twinned decahedral AuNCs, which comprises the following steps: preparing gold seeds: at room temperature, dissolving CTAC and citric acid in water to form a mixed solution, then adding HAuCl4 to the mixed solution, after mixing evenly, injecting NaBH4, then heating the solution to 85-90 °C and maintaining for 380-420 min, and then cooling to room temperature and continuing to age for 1-3 h to obtain gold seeds; preparing AuNCs: adding HAuCl4 to the BDAC solution, after mixing evenly, adding acid and AA aqueous solution to obtain a growth solution, and finally adding the gold seeds to the growth solution, and growing at a constant temperature of 30 °C for not less than 20 min to obtain quintuple twinned decahedral AuNCs; the preparation conditions are mild and the operation is simple; seeds with twin defects are prepared by controlling the concentration of sodium borohydride; the selection of the surfactant CTAC promotes the thermodynamic maturation during thermal aging and helps the transformation of single crystal seeds to polycrystals; and the adjustment of the pH value of the growth solution can control the change of the morphology of quintuple twinned decahedral AuNCs.

Description

Technical Field

[0001] The present invention relates to a method for preparing gold nanomaterials, and particularly to a method for preparing penta-twinned decahedral Au NCs. Background Art

[0002] Precious metals have a wide range of applications in catalysis, biomedicine, energy environment, etc. Their properties are closely related to their structure, morphology and size. Therefore, their controllable preparation has become a current research hotspot. Among them, the twins in Au NCs with a penta-twinned decahedral structure tend to generate at the grain boundaries and grow along a certain crystal direction. The obtained nanomaterials with a multiple twin structure have important applications in crystal growth, biological diagnosis, surface plasmon optics, etc. due to their special physical and chemical properties. Due to its five-fold symmetry, clear lattice structure, adjustable aspect ratio, etc., the penta-twin exhibits very rich optical properties in the visible-infrared region. Au NCs with a penta-twinned decahedral structure have attracted great attention from researchers in many fields due to their unique structure, optical, catalytic and other properties. In-depth exploration of their controllable preparation is of great significance for both theoretical research and practical applications. Au NCs have rich structures such as "hot spots", "edges", "steps" and "tips", making Au NCs have high surface-enhanced Raman scattering (SERS) performance. In order to make full use of the optical properties of Au NCs related to morphology and size, a method that can achieve mild preparation conditions and reproducibly prepare Au NCs with a uniform and stable morphology is an urgent requirement in the current material field.

[0003] The patent document with the publication number CN101357402B discloses a method for synthesizing decahedral gold nanoparticles. In this method, polyvinylpyrrolidone is used as a coating agent and N,N'-dimethylformamide is used as a reducing agent, and a microwave method is adopted to control the synthesis of decahedral gold nanoparticles. Polyvinylpyrrolidone is added to N,N'-dimethylformamide and stirred to dissolve; after polyvinylpyrrolidone is completely dissolved, chloroauric acid is added and stirred to obtain a reaction precursor solution; the reaction precursor solution is poured into a microwave reaction vessel and placed in a microwave heater for reaction, and the reaction system is naturally cooled to room temperature, and centrifuged to separate the synthesized gold nanoparticles from polyvinylpyrrolidone, and then washed to obtain a decahedral gold nanoparticle product. In this method, heating the reaction requires a high-temperature environment of 100-200°C, the preparation cost is relatively high, and the preparation conditions are relatively demanding. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a preparation method with mild preparation conditions and a stable morphology of the prepared penta-twinned decahedral Au NCs.

[0005] Technical solution: A preparation method of quintuple twin decahedral Au NCs according to the present invention includes the following steps:

[0006] (1) Preparation of gold seeds: At room temperature, CTAC (cetyltrimethylammonium chloride) and citric acid are dissolved in water to form a mixed solution, then HAuCl4 is added to the mixed solution, and after mixing evenly, NaBH4 is injected. Then the solution is heated to 85 - 90 °C and maintained for 380 - 420 min, and then cooled to room temperature and aged for 1 - 3 h to obtain gold seeds with quintuple twin edges;

[0007] (2) Preparation of quintuple twin decahedral Au NCs: HAuCl4 is added to a BDAC (octadecylbenzyldimethylammonium chloride) solution, and after mixing evenly, an acid and an AA (ascorbic acid) aqueous solution are added to obtain a growth solution. Finally, the gold seeds are added to the growth solution and grown at a constant temperature of 30 °C for not less than 20 min to obtain quintuple twin decahedral Au NCs.

[0008] Further, in step (1), the concentration ratio of CTAC, citric acid, HAuCl4 and NaBH4 is 277 - 278:27 - 28:1:833 - 834.

[0009] Further, in step (1), the molar concentration of CTAC is 48 - 52 mM.

[0010] Further, in step (1), the volume ratio of water to the NaBH4 solution is 28 - 29:1.

[0011] Further, in step (1), the concentration of the NaBH4 solution is 45 - 55 mM.

[0012] Further, in step (2), the pH value of the growth solution is lower than 2.2.

[0013] Further, in step (2), the acid is one of hydrochloric acid, nitric acid, sulfuric acid and acetic acid, and the acid is mainly used to adjust the pH value of the growth solution.

[0014] Further, in step (2), the concentration ratio of BDAC, HAuCl4, HCl and AA is 9 - 10:2 - 3:1:10.

[0015] Further, in step (2), the molar concentration of BDAC is 91 - 95 mM, preferably 93 mM; the molar concentration of HAuCl4 is 35 - 36 mM; preferably, the molar concentration of HCl is 12 M, 20 - 24 μL; the volume ratio of BDAC, HAuCl4, HCl, AA and the gold seed solution is 100:1:0.2:0.75.

[0016] Furthermore, the molar concentration of AA in step (2) is 91 - 95 mM.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0018] The method for preparing quintuple-twinned decahedral AuNCs of the present invention features stable and controllable AuNCs morphology, mild preparation conditions, and simple operation. By controlling the concentration of sodium borohydride, seeds with twin defects are prepared. A relatively low concentration and small volume of sodium borohydride may lead to unsuccessful seed preparation, while appropriate concentration and volume of sodium borohydride contribute to the successful preparation of seeds. The selection of surfactant CTAC promotes the thermodynamic maturation during thermal aging and helps the transformation from single-crystal seeds to polycrystals. Moreover, the adjustment of the pH value of the growth solution can control the change in the morphology of the final quintuple-twinned decahedral AuNCs. Description of the Drawings

[0019] Figure 1 Transmission electron microscopy (TEM) image of the quintuple-twinned gold seeds in Example 1;

[0020] Figure 2 Ultraviolet-visible absorption spectrum (UV-Vis) of the quintuple-twinned gold seeds in Example 1;

[0021] Figure 3 Scanning electron microscopy (SEM) image of the quintuple-twinned decahedral AuNCs in Example 1;

[0022] Figure 4 TEM image of the quintuple-twinned decahedral AuNCs in Example 1;

[0023] Figure 5 Transmission Kikuchi diffraction (TKD) image of the quintuple-twinned decahedral AuNCs in Example 1;

[0024] Figure 6 X-ray powder diffraction (XRD) pattern of the quintuple-twinned decahedral AuNCs in Example 1;

[0025] Figure 7 UV-Vis spectrum of the quintuple-twinned decahedral AuNCs in Example 1;

[0026] Figure 8 SEM image of the quintuple-twinned decahedral AuNCs in Example 2;

[0027] Figure 9 SEM image of the quintuple-twinned decahedral AuNCs in Example 3;

[0028] Figure 10SEM image of the five-twinned decahedral AuNCs of Example 4;

[0029] Figure 11 SEM image of the AuNCs of Comparative Example 1;

[0030] Figure 12 SEM image of the AuNCs of Comparative Example 2;

[0031] Figure 13 SEM image of the AuNCs of Comparative Example 3;

[0032] Figure 14 SEM image of the AuNCs of Comparative Example 4;

[0033] Figure 15 SEM image of the AuNCs of Comparative Example 5. Detailed implementation mode

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0035] In the following examples of the present invention, TEM images: obtained by TEM of JEOL-2100F (Japan) at a voltage of 200 KV. SEM images: obtained by SEM of JSM-7600F (Japan, JEOL). UV-vis test: obtained UV-vis spectra by Cary 60 spectrophotometer (Agilent, USA). XRD test: obtained XRD results by D / max 2500VL / PC diffractometer (Japan) (Japan), and the scanning range was 10 - 90°.

[0036] Example 1:

[0037] Preparation of five-twinned decahedral AuNCs based on gold seeds

[0038] (1) Preparation of gold seeds: First, add 10 mL of 50 mM CTAC and 5 mM citric acid into a 20 mL screw-cap glass bottle, and then add HAuCl4 to make its final concentration in the 10 mL solution 0.18 mM. Then, quickly add 0.35 mL of 50 mM ice-cold NaBH4 solution to the above mixed solution at one time, stir for 5 min, and then place it in an oil bath at 90 °C and keep it for 400 min.

[0039] (2) Preparation of penta-twinned decahedral Au NCs: First, add 10 mL of 93 mM BDAC into a 20 mL screw-cap glass bottle. Under magnetic stirring, add 0.1 mL of 21.3 mM HAuCl4. After the suspension becomes a clear light yellow solution, sequentially add 20 μL of 10 mM HCl and 0.075 mL of 100 mM AA. At this time, the pH value of the growth solution is 1.45. Add 0.10 mL of gold seeds into the growth solution within 1 minute. Finally, keep the obtained mixture at 30 °C for 30 min. Separate to obtain penta-twinned decahedral Au NCs.

[0040] Before use, centrifuge the synthesized Au NCs (5000 rpm, 15 min), and then redisperse them in an equal volume of ultrapure water. The obtained product was characterized by TEM ( Figure 1 , Figure 4 ), UV-Vis ( Figure 2 , Figure 7 ), SEM ( Figure 3 ), TKD ( Figure 5 ), and XRD ( Figure 6 ). It can be known that the obtained gold seeds have penta-twinned edges, and the final product is Au NCs with a penta-twinned decahedral structure.

[0041] Example 2

[0042] The specific preparation method is basically the same as that in Example 1, except that in step (1), the molar concentration of the NaBH4 solution is 45 mM, and 0.35 mL is added. At this time, the gold seeds prepared in step (1) are put into the growth solution according to the method in step (2) of Example 1 to prepare penta-twinned decahedral Au NCs, and SEM testing is carried out. As shown in Figure 8 , it can be seen that there are Au NCs with a penta-twinned decahedral structure.

[0043] Example 3

[0044] The specific preparation method is basically the same as that in Example 1, except that in step (1), the molar concentration of the NaBH4 solution is 55 mM, and 0.35 mL is added. At this time, the gold seeds prepared in step (1) are put into the growth solution according to the method in step (2) of Example 1 to prepare penta-twinned decahedral Au NCs, and SEM testing is carried out. The results are as shown in Figure 9 , and it can be seen that there are Au NCs with a penta-twinned decahedral structure.

[0045] Example 4

[0046] The specific preparation method is basically the same as that of Example 1, except that in step (2), the pH value of the growth solution is 2.2. The finally obtained AuNCs were characterized by SEM, and the results are as Figure 10 shown, and it can be seen that the AuNCs have a penta-twinned icosahedral structure.

[0047] Comparative Example 1

[0048] The specific preparation method is basically the same as that of Example 1, except that in step (2), hydrochloric acid is not added to the growth solution, and the pH value of the growth solution is 3.62. The finally obtained AuNCs were characterized by SEM, and the results are as Figure 11 shown. At this time, it can be seen that the shape of the AuNCs becomes significantly long and narrow, losing the penta-twinned icosahedral structure.

[0049] Comparative Example 2

[0050] The specific preparation method is basically the same as that of Example 1, except that 42 μL of 200 mM aqueous Na2CO3 solution is added to the growth solution environment, and the pH value of the growth solution in step (2) is 7.02. The finally obtained Au NCs were characterized by SEM, and the morphology is as Figure 12 shown.

[0051] Comparative Example 3

[0052] The specific preparation method is basically the same as that of Example 1, except that 72 μL of 200 mM aqueous Na2CO3 solution is added to the growth solution environment, and the pH value of the growth solution in step (2) is 9.53. The finally obtained AuNCs were characterized by SEM, and the morphology is as Figure 13 shown.

[0053] Comparative Example 4

[0054] The specific preparation method is basically the same as that of Example 1, except that in step (1), the molar concentration of the NaBH4 solution is 40 mM and the addition amount is 350 mL. The finally obtained Au NCs were characterized by SEM, and the results are as Figure 14 shown.

[0055] Comparative Example 5

[0056] The specific preparation method is basically the same as that of Example 1, except that in step (1), the molar concentration of the NaBH4 solution is 60 mM and the addition amount is 350 mL. The finally obtained Au NCs were characterized by SEM, and the results are as Figure 15 shown.

[0057] It can be seen from Examples 1 and 4, Comparative Examples 1, 2, and 3, and their corresponding drawings that as the pH of the growth solution increases, most of the morphologies of the grown Au NCs become long and narrow, and the prepared results are unstable with various morphologies. Therefore, the optimal pH value of the growth solution is below 2.2.

[0058] It can be seen from Examples 1, 2, and 3, Comparative Examples 4 and 5, and their corresponding drawings that when the concentration of the NaBH4 solution is in the range of 45 - 55 mM, the morphology of the prepared Au NCs is stable and has an obvious five-twin decahedral structure; when it is higher than or lower than this range, the morphology of the prepared Au NCs is significantly different and varies, without a stable morphology.

Claims

1. A preparation method of quintuple-twinned decahedral AuNCs, characterized in that, It includes the following steps: (1) Preparation of gold seeds: At room temperature, CTAC and citric acid are dissolved in water to form a mixed solution, then HAuCl4 is added to the mixed solution. After mixing evenly, NaBH4 is injected. Then the solution is heated to 85 - 90 °C and maintained for 380 - 420 min, and then cooled to room temperature and aged for 1 - 3 h to obtain gold seeds with five-fold twin edges; (2) Preparation of five-fold twin decahedral AuNCs: HAuCl4 is added to the solution of octadecylbenzyldimethylammonium chloride BDAC. After mixing evenly, an acid and an AA aqueous solution are added to obtain a growth solution. Finally, the gold seeds are added to the growth solution and grown at a constant temperature of 30 °C for no less than 20 min to obtain five-fold twin decahedral AuNCs; In step (1), the concentration ratio of CTAC, citric acid, HAuCl4 and NaBH4 is 277 - 278:27 - 28:1:833 - 834; the volume ratio of water and NaBH4 solution is 28 - 29:1; the concentration of the NaBH4 solution is 45 - 55 mM; In step (2), the pH value of the growth solution is lower than 2.

2.

2. The preparation method of the five-fold twinned decahedral AuNCs according to claim 1, wherein, The molar concentration of CTAC is 48 - 52 mM.

3. The preparation method of the five-fold twinned decahedral AuNCs according to claim 1, wherein, In step (2), the acid is one of hydrochloric acid, nitric acid, sulfuric acid and acetic acid.

4. The preparation method of the five-fold twinned decahedral AuNCs according to claim 3, characterized in that, The concentration ratio of BDAC, HAuCl4, HCl and AA is 9 - 10:2 - 3:1:

10.

5. The preparation method of the five-fold twin decahedral AuNCs according to claim 4, wherein, The molar concentration of BDAC is 91 - 95 mM, and the molar concentration of HAuCl4 is 35 - 36 mM.

6. The preparation method of the five-fold twinned decahedral AuNCs according to claim 4, characterized in that, The molar concentration of AA is 91 - 95 mM.

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