Influence of Reagents on the Synthesis Process and Shape of Silver Nanoparticles

The aim of this study was to prepare the silver nanoparticles (AgNPs) via chemical reduction and analyze the impact of used reduction agents: sodium borohydride (NaBH₄), trisodium citrate (TSC), polyvinylpyrrolidone (PVP), and hydrogen peroxide (H₂O₂) on the reduction rate of Ag⁺ ions to Ag⁰, and on nanoparticles shape. It was proven that combinations of reduction agents dramatically influence the synthesis rate of AgNPs and the color of solutions, which depends on the shape and size of nanoparticles. NaBH₄, TSC, and PVP showed good reduction power. In particular, TSC proved to be a key factor influencing the shape of AgNPs. The shape of nanoparticles influences the color of colloidal solutions. Yellow solutions, where UV-vis absorbance maxima (ABS_max) are in the wavelength interval 380-420 nm, contain spherical particles with a mean size of 25 nm, whereas the blue shift of ABS_max to wavelengths higher than 750 nm indicate the presence of triangular nanoparticles (size interval 18-150 nm). A mixture of spherical, triangular, irregular, and hexagonal nanoparticles give different color, e.g., green. The formation and stability of AgNPs was tracked by UV-vis spectroscopy, size and shape by TEM techniques, and particle size distribution was studied by particle size analyzer.