Effect of the Excitation Wavelength on the Photochemical Synthesis of Citrate-Capped Au Nanoparticles

We present a study on the photochemical reduction of gold ions for synthesizing citrate-capped Au nanoparticles (AuNP), employing UV (395 nm) and visible light of different wavelengths (473, 530, and 650 nm) from high-power LEDs. UV-Vis spectra of the samples obtained with different wavelengths and times of irradiation were analyzed to determine the stability of the colloidal solution of nanoparticles and the kinetics of the production of nanoparticles. For all the evaluated conditions, the photochemical reduction follows the known sigmoidal law, with a fast nucleation phase and a growing phase, where speed becomes slower with the increase of the wavelength. AuNPs were obtained at all the employed wavelengths; nevertheless, the formation process was less efficient using larger wavelengths, producing also agglomeration and less rounded AuNPs.