A method for coating silicon dioxide on both ends of gold nanorods

Abstract

The invention discloses a method for coating silicon dioxide at both ends of a gold nanorod, comprising the following steps: (1) preparing a gold nanorod dispersion by a seed growth method; (2) centrifuging the obtained gold nanorod dispersion, removing the supernatant, washing to obtain the gold nanorod, dispersing the gold nanorod in a CTAB solution, and obtaining a gold nanorod CTAB dispersion; (3) adjusting the pH of the gold nanorod CTAB dispersion to 8.5, adding a TEOS ethanol solution at one time under stirring, stirring for 2 days, centrifuging, washing the separated matter with water and ethanol, and dispersing it in ethanol to obtain gold nanorods with silicon dioxide coated at both ends. The synthesis method of the invention is simple and highly repeatable, and the obtained dumbbell-shaped silicon dioxide shell is used as a hard template and is not easily affected by environmental factors.

Description

Technical Field

[0001] The invention relates to the field of synthesis of metal nano materials, in particular to a method for coating silicon dioxide on both ends of a gold nanorod. Background Art

[0002] In recent years, precious metal nanoparticles have gradually become a key topic for researchers to explore. Among them, gold nanorods have attracted the interest of many fields such as sensors, catalysis, and biomedicine because of their very rich chemical and physical properties. However, compared with single-component nanostructured gold nanorods, the bimetallic structure can not only change its morphology, but also optimize its physical and chemical properties through the unique characteristics of the second metal. For example, coating the surface of gold nanorods with silver can enhance its resonance performance, and coating with platinum or palladium can have better catalytic ability, etc., so it has also attracted widespread attention and research. More importantly, the anisotropic growth of the second metal on the gold nanorods provides more possibilities for its new physical and chemical properties, can provide more abundant active sites, and further improve the catalytic activity and stability. The methods for the growth of the second metal mainly include the soft template method and the hard template method. The typical soft template method is that the molecules are selectively adsorbed on different faces of the nanoparticles. For example, CTAB is easily adsorbed on the side of the nanorod, while the concentration at both ends is relatively low, so that the second metal is preferentially precipitated at both ends. Although the soft template method has many applications, it is easily affected by thermodynamic and kinetic factors, such as the balance between adsorbed molecules and free molecules in the solution, the surface-dependent metal deposition rate and the molecular bonding strength, and becomes difficult to control. 2 As a hard template, the two ends of the gold nanorods are coated with silica shells to form a dumbbell shape, while the sides of the gold nanorods not coated with silica shells can further undergo metal regrowth to obtain anisotropic bimetallic materials, which are not easily affected by the external environment and have good stability.

[0003] The Chinese patent with application publication number CN202011631694.0 and application publication date December 30, 2020 discloses a preparation method for growing mesoporous silica material on the surface of gold nanorods, and obtains a gold nanorod structure coated with a core-shell structure silica shell. The main preparation method is as follows: using hexadecyltrimethylammonium bromide (CTAB) and sodium oleate (NaOL) as dual surfactants, the seed growth method is used to synthesize gold nanorods; the gold nanorods are centrifuged and redispersed in the CTAB solution, and after adding a certain amount of NaOH solution, TEOS solution is added 6 times at a time interval of 30 minutes, and stirring is continued for two days to obtain the final mesoporous silica material. The operation process of this method is complicated, the experimental time is long, and the synthesized structure can only improve the stability of metal regeneration. The method provided by this patent is only a one-step operation, the experiment is simple and time-saving, and the operability is strong. On the basis of enhancing the stability of the structure, anisotropic growth can also be achieved. Summary of the invention

[0004] The invention aims to provide a method for coating silicon dioxide at both ends of gold nanorods with a simple synthesis method and strong repeatability, thereby solving the problem that the soft template method is easily affected by thermal and dynamic factors.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for coating silicon dioxide at both ends of a gold nanorod of the present invention comprises the following steps:

[0007] (1) Gold nanorod dispersion was prepared using the seed growth method.

[0008] (2) Centrifuging the obtained gold nanorod dispersion, removing the supernatant, washing to obtain the gold nanorods, and dispersing the gold nanorods in a CTAB solution to obtain a gold nanorod CTAB dispersion.

[0009] (3) After adjusting the pH of the gold nanorod CTAB dispersion to 8.5, the TEOS ethanol solution was added all at once under stirring, stirred for 2 days, and centrifuged. The separated matter was washed with water and ethanol, and then dispersed in ethanol to obtain gold nanorods with silica coated at both ends.

[0010] Preferably, in step (1), the specific steps of preparing the gold nanorod dispersion by the seed growth method are: 4 After the solution and CTAB solution were mixed, NaBH 4 solution, stirring to obtain a seed solution; after dissolving the CTAB solution and NaOL in water, add AgNO 3 The solution was allowed to stand at a constant temperature and then HAuCl was added 4solution, stirring to obtain a growth solution; after adjusting the pH of the growth solution to 1.1-1.3, adding ascorbic acid solution and seed solution in sequence, heating in a water bath, and standing to obtain a gold nanorod dispersion.

[0011] Preferably, 0.025 mL of 0.1 M HAuCL 4 The solution was mixed with 10 mL of 0.1 M CTAB solution and stirred to obtain a seed solution; 0.6 mL of 0.01 M NaBH 4 Solution: Dissolve 2.5 mL of 0.1 M CTAB solution and 0.037 g of NaOL in 21.25 mL of water at 50 °C, cool to 30 °C, and add 0.9 mL of 4 mM AgNO 3 The solution was heated in a 30°C water bath, allowed to stand for 15 min, and 0.25 mL of 10 mM HAuCl was added. 4 The solution was stirred at 400 rpm for 60 min to obtain a growth solution; the pH of the growth solution was adjusted to 1.1-1.3 with 37% hydrochloric acid, 75 μL and 64 mM ascorbic acid solution and 40 μL seed solution were added in sequence, heated at a constant temperature of 30°C in a water bath, and allowed to stand for 12 h.

[0012] Preferably, in step (2), the gold nanorods are dispersed in a CTAB solution with a concentration of 0.15 mM, with the gold nanorods CTAB being preferred; in step (3), the pH of the gold nanorod CTAB dispersion is adjusted to 8.5 using a 0.1 M NaOH solution; in the TEOS ethanol solution, the volume percentage of TEOS is 20%, and the volume ratio of the gold nanorod CTAB dispersion to the TEOS ethanol solution is 100:1; when the TEOS ethanol solution is added, the stirring speed is 1200 to 1400 rpm; and the temperature is controlled at 25°C during stirring.

[0013] The present invention provides a method for coating silicon dioxide at both ends of a gold nanorod, which provides a stable hard template for the growth of a second metal. The present invention firstly prepares a gold nanorod with good monodispersity by a seed growth method, and then adds a trace amount of NaOH to the dispersed CTAB after centrifugal washing to form a weak alkaline environment, which is conducive to the hydrolysis of TEOS and the coating of SiO on the surface of the gold nanorod. 2 ; TEOS is added once, compared with the SiO 2 The shell is simple to operate and saves time. When adding TEOS, it must be stirred at high speed because TEOS reacts quickly. Avoid excessive addition of SiO 2 Independent nucleation.

[0014] Therefore, the present invention has the following beneficial effects:

[0015] (1) The synthesis steps are simple and reproducible, and the obtained dumbbell-shaped silica shell serves as a hard template and is not easily affected by environmental factors;

[0016] (2) As a solid material, silica is less likely to dissociate than the adsorbed molecules in the soft template, is more stable, does not affect the location of metal precipitation, has a better blocking effect, and is beneficial to the selective precipitation of the second metal;

[0017] (3) The second metal is regrown on gold nanorods coated with dumbbell-shaped silica shells. The anisotropic bimetallic material obtained is a morphological structure that is difficult to obtain using the soft template method. It can provide more special catalytic active sites and has broad application prospects in the fields of photocatalysis, electrocatalysis, fuel cells, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a transmission electron microscopy image of the gold nanorods covered with a dumbbell-shaped silica shell in Example 1.

[0019] Figure 2 This is a transmission electron microscope image of the gold nanorods covered with a dumbbell-shaped silica shell in Comparative Example 1.

[0020] Figure 3 This is a transmission electron microscope image of the gold nanorods covered with a core-shell structured silica shell of Comparative Example 2. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] Example 1

[0023] (1) Preparation of gold nanorod dispersion using seed growth method:

[0024] 0.025 mL, 0.1 M HAuCL 4 The solution was mixed with 10 mL of 0.1 M CTAB solution and stirred to obtain a seed solution; 0.6 mL of 0.01 M NaBH 4 Solution: Dissolve 2.5 mL of 0.1 M CTAB solution and 0.037 g of NaOL in 21.25 mL of water at 50 °C, cool to 30 °C, and add 0.9 mL of 4 mM AgNO 3 The solution was heated in a 30°C water bath, allowed to stand for 15 min, and 0.25 mL of 10 mM HAuCl was added. 4 The solution was stirred at 400 rpm for 60 min to obtain a growth solution; the pH of the growth solution was adjusted to 1.1 with 37% hydrochloric acid, 75 μL and 64 mM ascorbic acid solution and 40 μL seed solution were added in sequence, heated at a constant temperature of 30°C in a water bath, and allowed to stand for 12 h.

[0025] (2) The obtained gold nanorod dispersion is centrifuged, the supernatant is removed, and the gold nanorods are obtained after washing. The gold nanorods are dispersed in a CTAB solution with a concentration of 0.15 mM to obtain a gold nanorod CTAB dispersion with a concentration of 0.1 mM.

[0026] (3) After adjusting the pH value of the gold nanorod CTAB dispersion to 8.5 with 0.1 M NaOH solution, the TEOS ethanol solution was added at once under stirring at a speed of 1400 rpm. The volume percentage of TEOS in the TEOS ethanol solution was 20%, and the volume ratio of the gold nanorod CTAB dispersion to the TEOS ethanol solution was 100:1. After adding the TEOS ethanol solution, the mixture was stirred at 400 rpm at 25°C for 2 days and centrifuged. The separated material was washed with water and ethanol and then dispersed in ethanol to obtain gold nanorods with silica coated on both ends.

[0027] The transmission electron microscopy of the obtained gold nanorods coated with silica at both ends is as follows Figure 1 As shown. Figure 1 It can be seen that the average length of the gold nanorods is about 78nm, the aspect ratio is about 3.77, and the silica shell is wrapped at both ends, in a dumbbell shape with a thickness of about 17nm.

[0028] Comparative Example 1

[0029] The difference between Comparative Example 1 and Example 1 is that in step (3), the volume ratio of the gold nanorod CTAB dispersion to the TEOS ethanol solution is 100:2, and the rest is exactly the same as Example 1.

[0030] The transmission electron microscopy image of the obtained gold nanorods is shown in Figure 2 As shown, from Figure 2 It can be seen that the sides of the gold nanorods are covered with a thin silica shell, and their shape is not strictly dumbbell-shaped.

[0031] Comparative Example 2

[0032] The difference between Comparative Example 2 and Example 1 is that the ethanol solution of TEOS is added dropwise 6 times, and the rest is exactly the same as Example 1.

[0033] The obtained gold nanorods transmission electron microscopy image is shown in Figure 3 As shown. Figure 3 It can be seen that the obtained gold nanorods are gold nanorods with a core-shell structure.

[0034] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A method for coating both ends of a gold nanorod with silicon dioxide, characterized in that: The following steps are involved: (1) Preparing gold nanorod dispersion using a seed growth method; (2) centrifuging the obtained gold nanorod dispersion, removing the supernatant, washing to obtain the gold nanorods, and dispersing the gold nanorods in a CTAB solution to obtain a gold nanorod CTAB dispersion; (3) After adjusting the pH of the gold nanorod CTAB dispersion to 8.5, the TEOS ethanol solution was added at once under stirring, stirred for 2 days, centrifuged, and the separated matter was washed with water and ethanol, and then dispersed in ethanol to obtain gold nanorods with silica coated at both ends; In step (3), the pH of the gold nanorod CTAB dispersion is adjusted to 8.5 using a 0.1 M NaOH solution; the volume percentage of TEOS in the TEOS ethanol solution is 20%, and the volume ratio of the gold nanorod CTAB dispersion to the TEOS ethanol solution is 100:1; when the TEOS ethanol solution is added, the stirring speed is 1200-1400 rpm; and the temperature is controlled at 25°C during stirring; The addition of NaOH forms a weak alkaline environment, which is conducive to the hydrolysis of TEOS to coat SiO2 on the surface of gold nanorods; when TEOS is added at one time, high-speed stirring is performed to avoid independent nucleation of SiO2.

2. A method for coating silicon dioxide at both ends of a gold nanorod according to claim 1, characterized in that: In step (1), the specific steps of preparing the gold nanorod dispersion by the seed growth method are as follows: after mixing the HAuCL4 solution and the CTAB solution, adding the NaBH4 solution and stirring to obtain the seed solution; after dissolving the CTAB solution and NaOL in water, adding the AgNO3 solution, allowing to stand at a constant temperature, adding the HAuCl4 solution and stirring to obtain the growth solution; after adjusting the pH of the growth solution to 1.1-1.3, adding the ascorbic acid solution and the seed solution in sequence, heating in a water bath, and allowing to stand to obtain the gold nanorod dispersion.

3. A method for coating both ends of a gold nanorod with silicon dioxide according to claim 2, characterized in that: Mix 0.025mL of 0.1M HAuCL4 solution and 10mL of 0.1M CTAB solution, and stir to obtain a seed solution; add 0.6mL of 0.01M NaBH4 solution; dissolve 2.5mL of 0.1M CTAB solution and 0.037g of NaOL in 21.25mL of water at 50°C, cool to 30°C, add 0.9mL of 4mM AgNO3 solution, heat at 30°C in a water bath, let stand for 15min, add 0.25mL of 10mM HAuCl4 solution, stir at 400rpm for 60min, and obtain a growth solution; adjust the pH of the growth solution to 1.1-1.3 with 37% hydrochloric acid, add 75μL of 64mM ascorbic acid solution and 40μL of seed solution in sequence, heat at 30°C in a water bath, and let stand for 12h.

4. A method for coating both ends of a gold nanorod with silicon dioxide according to claim 1, characterized in that: In step (2), the gold nanorods are dispersed in a CTAB solution with a concentration of 0.15 mM, and the concentration of the gold nanorods in the gold nanorod CTAB dispersion is 0.1 mM.

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