Microemulsions as templates for the synthesis of metallic nanoparticles

We synthesized platinum (Pt), bismuth (Bi), and lead (Pb) nanoparticles by using water-in-oil microemulsions as templates. The microemulsion chosen consisted of H2O/salt–n-decane–AOT/SDS–1-butanol while the salt was either the metal precursor (H2PtCl6, Bi(NO3)3, or Pb(NO3)2) or the reducing agent (NaBH4). As the size and the structure of the resulting nanoparticles are expected to depend on the size and structure of the templating microemulsion, we studied the phase behaviour of the templating microemulsion, i.e. the composition ranges in which spherical water-in-oil microemulsions are formed. The challenge was to find those conditions under which the microemulsions containing the metal precursor and the reducing agent, respectively, had the same size and structure. Nanoparticles of the metals (Pt, Bi, and Pb) were then synthesized by mixing these two microemulsions. The size and structure of the resulting particles were characterized by scanning electron microscopy (SEM) and X-ray powder diffractometry. Average crystallite sizes of D ≈ 5, 25, and 25 nm were found for Pt, Bi, and Pb particles, respectively. According to SEM images, these particles form clusters of several hundreds of nanometers.