A template-free method for ultrafast preparation of gold nanoflowers

Abstract

This invention provides a template-free method for ultrafast preparation of gold nanoflowers, which does not require the addition of surfactants, has a fast preparation speed, and exhibits high sensitivity to H2S. Moreover, the maximum absorption wavelength of the prepared gold nanoflowers remains essentially unchanged within the pH range of 1-6 and the temperature range of 5-55℃, making it suitable for various applications.

Description

Technical Field

[0001] This invention relates to the field of gold nanoflower preparation, and more particularly to a template-free ultrafast method for preparing gold nanoflowers. Background Technology

[0002] Currently, the preparation methods for gold nanoflowers are mainly classified into several categories, including the seed method, the template method, and the electrochemical method. The seed method requires the synthesis of gold seeds first, which is relatively cumbersome and time-consuming. The template method requires the preparation and removal of the template, which is also a complex process. The electrochemical method directly reduces gold ions to form nanoflower structures by adjusting the voltage and electrolyte composition in an electrolyte containing gold salts. In addition, most of the above traditional methods require the introduction of surfactants such as hexadecyltrimethylammonium bromide (CTAB). Summary of the Invention

[0003] To address the above problems, this invention provides a template-free method for ultrafast preparation of gold nanoflowers, which does not require the addition of surfactants and has a fast preparation speed.

[0004] The objective of this invention is achieved in the following manner: a template-free ultrafast method for preparing gold nanoflowers, comprising mixing 75-90 μL of HAuCl4 solution with a concentration of 25 mM and 4.6-4.9 mL of H2O at 10-30°C until homogeneous, and after 2-5 min, adding 0.13 mL of 1,7-naphthol solution with a concentration of 20-60 mM, the solution pH being 3-7, and reacting for 2-30 min.

[0005] Mix 75-90 μL of HAuCl4 solution (25 mM) with 4.6-4.9 mL of H2O at 20-30 °C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (20-30 mM). The pH of the solution should be 5-6. React for 3-30 min.

[0006] The solvent for HAuCl4 solution is water, and the solvent for 1,7-naphthol solution is a mixture of ethanol and water with a volume ratio of ethanol to water of 3 / 2.

[0007] Mix 75 μL of HAuCl4 solution (25 mM) with 4.79 mL of H2O at 20-30°C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (30 mM) with pH 6 and react for 3-6 min.

[0008] Compared with existing technologies, this invention provides a template-free method for ultrafast preparation of gold nanoflowers, which does not require the addition of surfactants, has a fast preparation speed, and exhibits high sensitivity to H2S. Moreover, the maximum absorption wavelength of the prepared gold nanoflowers remains essentially unchanged within the pH range of 1-6 and temperature range of 5-55℃, making it suitable for applications. Attached Figure Description

[0009] Figure 1 The following is a graph showing the results of the optimization experiments for reaction time and solution pH: Figure 1 A is the UV-Vis absorption spectrum of the product prepared at different reaction times; Figure 1 B is the UV-Vis absorption spectrum of the product prepared under different pH conditions.

[0010] Figure 2 The figure shows the optimized experimental results for chloroauric acid volume and 1,7-naphthol concentration: Figure 1 A is the UV-Vis absorption spectrum of the product prepared under different volume conditions of chloroauric acid; Figure 1 B is the UV-Vis absorption spectrum of the product prepared under different concentrations of 1,7-naphthol.

[0011] Figure 3 A and B are TEM and HAADF-STEM images of the gold nanoflowers prepared in Example 1, respectively. C and D are the distribution maps of Au and O elements in the gold nanoflowers prepared in Example 1, respectively, as shown by EDS mapping.

[0012] Figure 4 A and B are the XPS high-resolution photoelectron spectra of Au 4f and O 1s of AuNFs prepared in Example 1, respectively.

[0013] Figure 5 This is the XPS full spectrum of AuNFs prepared in Example 1.

[0014] Figure 6 The images show the FT-IR spectra of 1,7-naphthol (black line) and AuNFs prepared in Example 1 (red line).

[0015] Figure 7 This is a product prepared using sodium borohydride as a reducing agent, and its ultraviolet-visible absorption spectrum.

[0016] Figure 8 This is a product prepared using ascorbic acid as a reducing agent, and its ultraviolet-visible absorption spectrum.

[0017] Figure 9 This is a product prepared using glutathione as a reducing agent, and its ultraviolet-visible absorption spectrum.

[0018] Figure 10 This is a product prepared using tannic acid as a reducing agent, and its ultraviolet-visible absorption spectrum.

[0019] Figure 11 These are products prepared using sodium borohydride, ascorbic acid, glutathione, and tannic acid as reducing agents, along with their UV-Vis absorption spectra.

[0020] Figure 12 A and B are the UV-Vis absorption spectra of the gold nanoflowers prepared in Example 1, detected at different pH (1-6) and different temperatures (5-55℃).

[0021] Figure 13 These are the UV-Vis absorption spectra of products prepared by adding different amounts of CTAB.

[0022] Figure 14 Figure A shows the UV-Vis absorption spectra of the product prepared in Example 1 with different concentrations of H2S added. The arrows in the figure pass through the curves from top to bottom, and the H2S concentrations corresponding to the curves gradually increase. Figure B shows the absorbance of the H2S concentration and the corresponding UV absorption peaks of the product prepared in Example 1 in Figure A. Detailed Implementation

[0023] A template-free ultrafast method for preparing gold nanoflowers involves mixing 75-90 μL of HAuCl4 solution (25 mM) with 4.6-4.9 mL of H2O at 10-30 °C for 2-5 min. Then, 0.13 mL of 1,7-naphthol solution (20-60 mM) is added, with a pH of 3-7. The reaction is carried out for 2-30 min.

[0024] Mix 75-90 μL of HAuCl4 solution (25 mM) with 4.6-4.9 mL of H2O at 20-30 °C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (20-30 mM). The pH of the solution should be 5-6. React for 3-30 min.

[0025] The solvent for HAuCl4 solution is water, and the solvent for 1,7-naphthol solution is a mixture of ethanol and water with a volume ratio of ethanol to water of 3 / 2.

[0026] Mix 75 μL of HAuCl4 solution (25 mM) with 4.79 mL of H2O at 20-30°C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (30 mM) with pH 6 and react for 3-6 min.

[0027] The present invention will now be described in detail with reference to specific embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the present invention. Example 1

[0028] A template-free ultrafast method for preparing gold nanoflowers involves mixing 75 μL of HAuCl4 aqueous solution (25 mM) with 4.79 mL of H2O at room temperature (25 ± 1 ℃). After 2 min, 0.13 mL of 1,7-naphthyldiol solution (30 mM) is added to the solution. The pH of the HAuCl4 and naphthyldiol mixture is 6. After 3 min, the solution changes from light yellow to blue, indicating successful preparation of gold nanoflowers (AuNFs). The 1,7-naphthyldiol solution is a mixture of ethanol and water in a volume ratio of 3 / 2.

[0029] (I) Condition Optimization Experiment The preparation method in Example 1 involved reacting under optimal conditions, specifically adjusting the volume of chloroauric acid, the concentration of 1,7-naphthol, the solution pH, and the reaction time. Under these optimal conditions, i.e., according to Example 1, the volume of chloroauric acid, the concentration of 1,7-naphthol, the solution pH, and the reaction time were varied, while other conditions remained constant. The UV-Vis absorption spectra of the solutions after the reaction are shown below. Figures 1-2 As shown.

[0030] Figure 1 The absorbance was low at 1 minute of reaction A, indicating an incomplete reaction. The absorbance reached its maximum at 3 minutes, at which point *Gynostemma pentaphyllum* was successfully synthesized. The absorbance remained essentially constant as the reaction time increased. Figure 1 B exhibits the highest absorbance at its characteristic absorption peak of 600 nm at pH=6 (without acid-base optimization). Figure 2 At the characteristic absorption peak of 600 nm, AB exhibits the highest absorbance at 75 µL of chloroauric acid (25 mM) and 30 mM of 1,7-naphthol as the reducing agent. Therefore, the optimal conditions are 3 min of reaction, pH=6, 75 µL of chloroauric acid (25 mM), and 30 mM of 1,7-naphthol as the reducing agent, resulting in the highest yield, uniform particle size, and good dispersibility.

[0031] (ii) AuNFs were successfully prepared To demonstrate the successful synthesis of AuNFs in Example 1, we used TEM, HAADF-STEM, XPS, and FT-IR to study the optimal experimental conditions ( Figure 1 and Figure 2 The four optimization conditions) were used to characterize the AuNFs prepared according to Example 1.

[0032] TEM showed that the prepared AuNFs material was flower-shaped. Figure 3 AuNFs exhibited good dispersion and uniform size, with an average size of 126.9 nm ± 5.1 nm. Furthermore, dark-field scanning transmission electron microscopy (HAADF-STEM) images showed that the prepared AuNFs appeared bright white with high contrast in the dark. Figure 3 B) reflects its flower-like morphology and uniform size, while the uniformity of dark field contrast also indicates that the compositional distribution of AuNFs is relatively uniform.

[0033] Furthermore, the EDS mapping results clearly show the presence of Au and O elements. Figure 3 CD). Especially the mapping signal of element O ( Figure 3 D) Uniformly distributed on the surface of AuNFs, confirming that 1,7-naphthol (O element) was successfully stabilized on the surface of BSA-AgAuNFs, serving both as a reducing agent for AuNFs preparation and as a stabilizer for AuNFs.

[0034] To further confirm the elemental composition and valence state of AuNFs, we performed XPS analysis on 1,7-naphthyldiol-stabilized AuNFs. AuNFs ((Au 4f 5 / 2 (88.28 eV) and 4f 7 / 2 The binding energy of Au (84.56 eV) indicates that Au 0 Atoms are dominant ( Figure 4 A). Furthermore, the binding energies of AuNFs (O1SCO (533.37 eV) and O1SC=O (531.67 eV)) are... Figure 4 B) This further indicates that 1,7-naphthol serves both as a reducing agent and a stabilizing agent (CO) in the preparation of AuNFs.

[0035] Furthermore, the affinity energies of C 1s, O 1s, and Au 4f are 285.21 eV, 533.27 eV, and 85.00 eV, respectively. Figure 5 The presence of C, O, and Au was confirmed, and 1,7-naphthol was further confirmed as a reducing agent and stabilizer in the preparation of AuNFs.

[0036] Subsequently, the infrared spectrum of AuNFs was measured. For example... Figure 6As shown by the red line, the two strong absorption bands at 3429 cm⁻¹ and 1622 cm⁻¹ are attributed to the stretching vibration of the phenolic hydroxyl group (OH) and the stretching vibration of the aromatic ring C=C skeleton, respectively, further confirming the successful preparation of 1,7-naphthiodiol-stabilized AuNFs using a template-free method. It is noteworthy that our new method for preparing AuNFs only requires the addition of 1,7-naphthiodiol and chloroauric acid, eliminating the need for templates (such as protein templates) and other surfactants (such as hexadecyltriammonium bromide), greatly simplifying the preparation of AuNFs.

[0037] (III) Uniqueness of the preparation method In the preparation of AuNFs, 1,7-naphthol is used as both a reducing agent and a stabilizer, resulting in better stability of the prepared AuNFs.

[0038] Figures 7-10 According to Example 1, the reducing agent 1,7-naphthol was replaced with ascorbic acid, tannic acid, sodium borohydride, and glutathione. The concentrations of ascorbic acid, tannic acid, sodium borohydride, and glutathione were all 30 mM, and the volume was 0.13 mL. The pH of the mixed solution of HAuCl4 and the reducing agent was adjusted to 6 using a 0.01 mol / L citric acid aqueous solution. The solvent for ascorbic acid, tannic acid, sodium borohydride, and glutathione was deionized water.

[0039] like Figures 7-11 Other types of reducing agents cannot replace 1,7-naphthyldiol in the preparation of AuNFs. For example... Figure 7 Sodium borohydride is an inorganic small-molecule reducing agent. The solution reacting with chloroauric acid is purple-red in color, with a UV absorption peak in the range of 510–530 nm. Therefore, it cannot induce chloroauric acid to form gold nanoflower structures, but only generates isotropic spherical gold nanoparticles; for example… Figure 8 Ascorbic acid is a small organic molecule reducing agent. The solution reacting with chloroauric acid is grayish-purple in color, with a UV absorption peak in the range of 520-540 nm. Therefore, the reaction with chloroauric acid can only produce spherical gold nanoparticles, not gold nanoflowers. Figure 9 Glutathione is an organic small molecule reducing agent. The solution reacting with chloroauric acid is a classic wine-red color, typical of spherical gold nanoparticles, with a UV absorption peak in the range of 530–570 nm. Therefore, it cannot induce chloroauric acid to form gold nanoflower structures, but only generates isotropic spherical gold nanoparticles; for example... Figure 10 Tannic acid is an organic macromolecular reducing agent. The solution after the reaction is rose-red in color, and the wavelength range of the ultraviolet absorption peak is between 520 and 560 nm. It produces spherical gold nanoparticles, rather than gold nanoflowers.

[0040] In summary, ascorbic acid, tannic acid, sodium borohydride, and glutathione only possess reducing power and lack morphology guiding effects, producing isotropic spherical gold nanoparticles that cannot form the branched structure of gold nanoflowers. Therefore, conventional reducing agents cannot achieve the directed synthesis of 1,7-naphthol in the preparation of gold nanoflowers, making 1,7-naphthol irreplaceable in inducing anisotropic growth of gold atoms and preparing gold nanoflowers.

[0041] (iv) Stability of the prepared AuNFs Finally, we measured the stability of the AuNFs prepared in Example 1 under different temperature and pH conditions.

[0042] like Figure 12 As shown in A and 12B, the maximum absorption wavelength of AuNFs is almost unaffected by changes in temperature (5-55 °C) and pH (1.0-6.0), indicating that the AuNFs prepared in this application are stable, which is beneficial for the use of gold nanoflowers.

[0043] like Figure 13 As shown, based on Example 1, adding the surfactant CTAB to prepare gold nanoflowers resulted in inhibiting the growth of gold nanoflowers or altering their surface structure. Therefore, the optimal conditions were achieved without using CTAB.

[0044] CTAB is typically used as a surfactant in the synthesis of gold nanoflowers. Therefore, CTAB was selected as the surfactant in this experiment. The specific procedure was as follows: 75 μL of HAuCl4 solution (25 mM) was mixed with 4.79 mL of H2O at room temperature. After 2 min, 5 μL of CTAB solution was added. The solvent for CTAB was H2O, and the concentrations were 5 mM, 10 mM, and 20 mM, respectively. After stirring at room temperature for 5-10 min to mix evenly, 0.13 mL of 1,7-naphthol solution (25 mM) was added. The pH of the solution was in the range of 3-6, and the reaction was carried out for 3 min. This was used to study the effect of the surfactant on the preparation of gold nanoflowers.

[0045] in addition Figure 13 The experiment with 0 mM is a blank control experiment without the surfactant CTAB. The procedure is as follows: A template-free ultrafast method for preparing gold nanoflowers involves mixing 75 μL of HAuCl4 aqueous solution (25 mM) with 4.79 mL of H2O at room temperature (25 ± 1 ℃). After 2 min, 0.13 mL of 1,7-naphthol solution (30 mM) is added to the above solution, and the reaction is allowed to proceed for 3 min. The results are as follows Figure 13As shown, when the CTAB concentration is in the range of 5-10 mM, the absorbance decreases significantly, indicating that a small amount of CTAB inhibits the growth of gold nanoflowers. The absorption peak position of high-concentration CTAB shifts significantly, indicating that high-concentration CTAB significantly changes the morphology of gold flowers. In summary, it can be concluded that the optimal synthesis conditions are without CTAB.

[0046] (V) Application Effects The 150 µL gold nanoflower solution prepared according to Example 1 was then mixed with 165 µL of PBS (pH 5.5) to adjust the pH of the solution to 5.5. Then, 35 µL of H2S of different concentrations (1 µM, 5 µM, 10 µM, 30 µM, 50 µM, and 100 µM) was added. After reacting for 20 min, the UV absorption spectrum was measured.

[0047] Figure 14 The solution used for blank detection in A was: 150 µL gold nanoflower solution + 165 µL PBS + 35 µL H2O; compared to the above addition of H2S, only 35 µL H2S was replaced with 35 µL H2O.

[0048] like Figure 14 As shown in Figure A, the absorbance of gold nanoflowers at 600 nm gradually decreases with increasing H2S concentration (1-100 µM). The regression equations are A... 600 =0.4779-0.0024[H2S](0-30 µM), where R 2 =0.985 and A 600 =0.4240-0.0006[H2S](30-100 µM), its R 2 =0.999 (as shown in Figure B), indicating that the decrease in absorbance is linearly related to the concentration of H2S.

[0049] The gold nanoflowers prepared in this application exhibit good response to H2S in the range of 1~100 µM, with a detection limit as low as 1 µM, indicating that the gold nanoflowers prepared in this application have high sensitivity to H2S.

[0050] Therefore, the template-free ultrafast method for preparing gold nanoflowers provided by this invention does not require the addition of surfactants, has a fast preparation speed, and exhibits high sensitivity to H2S. Moreover, the maximum absorption wavelength of the prepared gold nanoflowers remains essentially unchanged within the pH range of 1-6 and temperature range of 5-55℃, making it suitable for application.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art and any person skilled in the art, any equivalent substitutions or changes made to the technical solution and inventive concept of the present invention without departing from the overall concept of the present invention, as well as any changes and improvements made, should also be considered within the scope of protection of the present invention.

Claims

1. A template-free ultrafast method for preparing gold nanoflowers, characterized in that: Mix 75-90 μL of HAuCl4 solution (25 mM) with 4.6-4.9 mL of H2O at 10-30°C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (20-60 mM) with a pH of 3-7 and react for 2-30 min.

2. The method for ultrafast preparation of gold nanoflowers without templates according to claim 1, characterized in that: Mix 75-90 μL of HAuCl4 solution (25 mM) with 4.6-4.9 mL of H2O at 20-30 °C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (20-30 mM). The pH of the solution should be 5-6. React for 3-30 min.

3. The method for ultrafast preparation of gold nanoflowers without templates according to claim 1, characterized in that: The solvent for HAuCl4 solution is water, and the solvent for 1,7-naphthol solution is a mixture of ethanol and water with a volume ratio of ethanol to water of 3 / 2.

4. The method for ultrafast preparation of gold nanoflowers without templates according to claim 1, characterized in that: Mix 75 μL of HAuCl4 solution (25 mM) with 4.79 mL of H2O at 20-30°C until homogeneous. After 2-5 min, add 0.13 mL of 1,7-naphthol solution (30 mM) with pH 6 and react for 3-6 min.

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