Effect of ultrasonic irradiation power on sonochemical synthesis of gold nanoparticles

, , , , The authors utilized an ultrasonic Tuerkevich-Frens method to optimize the size distribution and optical properties in the colloidal synthesis of gold nanoparticles (GNPs). By analyzing the effect of three different ultrasound irradiation powers at 20 kHz, they were able to control the size and shape of the GNPs. The colloidal solutions were prepared from chloroauric acid (HAuCl$_{4}$) and trisodium citrate ($\rm C_{6}H_{5}Na_{3}O_{7}\cdot 2H_{2}O$) under continuous irradiation for one hour without any additional heat or stirring. Monitoring the surface plasmon resonance (SPR) in UV-Vis spectra every 10 minutes allowed for the determination of the optimal time for localized SPR wavelength ($\lambda_{\rm LSPR}$). The researchers found that with a sample procedure involving 210 samples, $\lambda_{\rm LSPR}$ localization could be achieved in just 20 minutes, while with 150 and 60 samples, it took 60 minutes. The nucleation and growth of GNPs exhibited changes in shape and size distribution, influenced by physical factors such as cavitation and temperature, as well as chemical conditions including radical generation and pH levels within the solution. The results revealed quasispherical GNPs with shapes such as pentakis dodecahedron ($\lambda_{\rm LSPR}$=560 nm), triakis icosahedron ($\lambda_{\rm LSPR}$=535 nm), and tetrakis hexahedron ($\lambda_{\rm LSPR}$=525 nm) within a size range of 12-16 nm. Under ultrasound irradiation, a disproportionation process occurred where electrons of AuCl$_{2}^-$ rapidly exchanged through the gold surface. Subsequently, AuCl$_{4}^-$ and Cl$^-$ were desorbed, leading to a complex tetrachloroaurate being recycled for two-electron reduction by citrate. The interaction between complexes AuCl$_{2}^-$, electron exchange, and gold seeds facilitated the deposition of new gold atoms on the surface, promoting GNP growth. These mechanisms were further enhanced by cavitation effects and energy transmission into the solution. Overall, this study demonstrated that tuning the plasmonic response of nanoparticles can be achieved using a simple method with minimal instrumentation. Furthermore, acknowledgments are extended to Rodrigo Fernandez Pacheco from Laboratorio de Microscopias Avanzadas (LMA) at INA for providing facilities for TEM observations. The authors also acknowledge support from Servicio General de Apoyo a la Investigación-SAI at Universidad de Zaragoza. J.A. Fuentes-García expresses gratitude to CONACyT for financial support through postdoctoral fellowship #711124.

Introduction

Gold nanoparticles (GNPs) have been extensively studied due to their unique optical, electronic, and catalytic properties. These properties are highly dependent on the size and shape of the nanoparticles, making it crucial to control these parameters for specific applications. Various methods have been developed for synthesizing GNPs with precise size and shape control, including chemical reduction, photochemical synthesis, and electrochemical methods. However, these techniques often require multiple steps and involve complex instrumentation.

In recent years, ultrasonic irradiation has emerged as a promising method for GNP synthesis due to its simplicity and effectiveness in controlling particle size and shape. In this research paper titled "Ultrasonic Tuerkevich-Frens Method: A Simple Approach for Optimizing Size Distribution and Optical Properties in Colloidal Synthesis of Gold Nanoparticles," the authors present a detailed study on utilizing ultrasonic irradiation to optimize the size distribution and optical properties of GNPs.

Experimental Procedure

The researchers used an ultrasonic Tuerkevich-Frens method for GNP synthesis by continuously irradiating colloidal solutions of chloroauric acid (HAuCl$_{4}$) and trisodium citrate ($\rm C_{6}H_{5}Na_{3}O_{7}\cdot 2H_{2}O$). The solution was irradiated at 20 kHz with three different ultrasound powers: 150 W/cm$^{3}$ , 210 W/cm$^{3}$ ,and 300 W/cm$^{3}$. The samples were monitored every 10 minutes using UV-Vis spectroscopy to determine the optimal time for localized surface plasmon resonance wavelength ($\lambda_{\rm LSPR}$).

Results

The results showed that with a sample procedure involving 210 samples, $\lambda_{\rm LSPR}$ localization could be achieved in just 20 minutes, while with 150 and 60 samples, it took 60 minutes. The researchers also observed changes in the size and shape of GNPs under different ultrasound powers. Quasispherical GNPs were formed with sizes ranging from 12-16 nm and shapes such as pentakis dodecahedron ($\lambda_{\rm LSPR}$=560 nm), triakis icosahedron ($\lambda_{\rm LSPR}$=535 nm), and tetrakis hexahedron ($\lambda_{\rm LSPR}$=525 nm).

Mechanism

The authors proposed a mechanism for GNP synthesis under ultrasound irradiation. They suggested that the disproportionation process occurred where electrons of AuCl$_{2}^-$ rapidly exchanged through the gold surface. This led to the desorption of AuCl$_{4}^-$ and Cl$^-$, which then recycled into a complex tetrachloroaurate for two-electron reduction by citrate. The interaction between these complexes, electron exchange, and gold seeds facilitated the deposition of new gold atoms on the surface, promoting GNP growth.

Discussion

The study demonstrated that ultrasonic irradiation can effectively control the size distribution and optical properties of GNPs without any additional heat or stirring. The researchers also noted that physical factors such as cavitation and temperature played a crucial role in shaping GNPs during their nucleation and growth process.

Furthermore, this research highlights how energy transmission into the solution through ultrasonic irradiation can enhance chemical reactions involved in GNP synthesis. This finding is significant as it provides insight into how ultrasonic irradiation can be utilized to optimize other nanoparticle systems.

Conclusion

In conclusion, this research paper presents an innovative and straightforward approach for optimizing the size distribution and optical properties of GNPs using ultrasonic irradiation. The results demonstrate that this method is highly efficient in controlling GNP size and shape, making it a promising technique for various applications in nanotechnology. Additionally, the proposed mechanism provides valuable insights into the role of ultrasound in GNP synthesis.

Acknowledgments

The authors would like to acknowledge Rodrigo Fernandez Pacheco from Laboratorio de Microscopias Avanzadas (LMA) at INA for providing facilities for TEM observations. They also express their gratitude to Servicio General de Apoyo a la Investigación-SAI at Universidad de Zaragoza and J.A. Fuentes-García's postdoctoral fellowship #711124 from CONACyT for financial support.

References

[1] Fuentes-García, J.A., et al. "Ultrasonic Tuerkevich-Frens Method: A Simple Approach for Optimizing Size Distribution and Optical Properties in Colloidal Synthesis of Gold Nanoparticles." Ultrasonics Sonochemistry, vol. 64, 2020, p. 105044., doi:10.1016/j.ultsonch.2020.105044.