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Effect of ultrasonic irradiation power on sonochemical synthesis of gold nanoparticles

In this work, optimized size distribution and optical properties in colloidal synthesis of gold nanoparticles (GNPs) were obtained using a proposed ultrasonic Tuerkevich-Frens method. The effect of three ultrasound (20 kHz) irradiation powers has been analyzed as size and shape control parameter. The GNPs colloidal solutions were obtained 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 1 hour without any heat or stirring. The surface plasmon resonance (SPR) was monitored in the UV-Vis spectra every 10 minutes to found the optimal time for localized SPR wavelength ($λ_{\rm LSPR}$) and the 210 sample procedure reduces the $λ_{\rm LSPR}$ localization to 20 minutes, while 150 and 60 samples show $λ_{\rm LSPR}$ in 60 minutes. The nucleation and growth of GNPs showed changes in shape and size distribution, which were associated with physical (cavitation, temperature) and chemical (radical generation, pH) conditions in the solution. The results showed quasispherical GNPs as pentakis dodecahedron ($λ_{\rm LSPR}$=560 nm), triakis icosahedron ($λ_{\rm LSPR}$=535 nm), and tetrakis hexahedron ($λ_{\rm LSPR}$= 525 nm) in a size range from 12-16 nm. US irradiation induced a disproportionation process, electrons of AuCl$_{2}^-$ rapidly exchanged through the gold surface. After AuCl$_{4}^-$ and Cl$^-$ are desorbed and a complex tetrachloroaurate is recycled for the two-electron reduction by citrate, aurophilic interaction between complexes AuCl$_{2}^-$, electrons exchange and gold seeds, the deposition of new gold atoms on the surface promoting the growth of GNPs. These mechanisms are enhanced by the cavitation effects and transmitted energy into the solution, showing that the plasmonic response from our nanoparticles can be tuned with this simple method and minimum intrumentation.