Synthesis of Silver Nanoparticles Using Different Silver Phosphine Precursors: Formation Mechanism and Size Control

Silver nanoparticles (AgNPs) ranging from 2.5 to 7.1 nm in diameter with a narrow size distribution are prepared by reducing different silver phosphine precursors RAg(PPh3)(n) (R = Cl, Br, or NO3 and n = 1 or 3) with tert-butylamine borane (TBAB) in the presence of dodecanethiols (C-12) at a temperature between 100 and 160 degrees C. The study of the formation process of AgNPs by UV-vis and IR spectroscopy reveals that the phosphine (PPh3) derived from the metal precursor and thiols coat the NPs surface. In addition, the PPh3/C-12 ligand ratio is shown to decrease during the NPs growth. PPh3 is indeed progressively replaced by thiols. The rate of the PPh3-thiols exchange is shown to depend on the nature of the silver precursor and to influence the final NPs size. By using NO3Ag(PPh3), the surface poisoning by PPh3 is shown to be the most efficient, leading to the smallest NPs size (2.5 nm in diameter). Furthermore, we get evidence that the nanoparticle size is controlled by the nature of R in the precursor. Finally, it is found that the influence of the reaction temperature and the thiol chains length on the final NPs size depends on the silver precursor used.