Colloidal synthesis of copper nanoparticles in a two-phase liquid–liquid system

Synthesis of copper nanoparticles in a two-phase, toluene–water system was investigated. The synthesis involves a transfer of metal cations from the aqueous phase to the toluene phase through the use of tetraoctylammonium bromide, a phase transfer reagent. Subsequently, the metal cations were reduced using sodium borohydride in the presence of oleylamine, a stabilizing ligand. Due to the high tendency of copper to oxidize in air, the syntheses and post-synthesis treatments were carried out in an inert atmosphere, N2. Non-agglomerated, generally spherical, copper nanoparticles with a mean size of 6.06 nm were successfully made using the technique. By analyzing the lattice d spacing of HRTEM images, the crystal structure of the particles was found to be FCC. The expected plasmon resonance peak for copper, 570 nm, was missing from UV/Vis spectroscopy analysis; this has been attributed to quenching due to residual CuBr.