Controlled Design of Size-Tunable Monodisperse Nickel Nanoparticles

Abstract

We present here a complete study on a synthesis of nickel nanoparticles involving the reaction of [Ni(acac) 2 ] with oleylamine (OA) and trioctylphosphine (TOP) reactants, whose simultaneous presence and relative amounts are paramount. The role of every reactant in the nucleation and growth of the nanoparticles has been delineated: OA is the reductant and thus controls the nucleation rate, meanwhile TOP provides a tunable surface stabilization through coordination on the Ni(0) surface. This result leads us to a design synthesis providing tailored monodispersed nanoparticles in a wide range (2−30 nm), which allows self-consistent studies of size-induced changes in catalytic and magnetic properties. Additionally, the growth mechanism is demonstrated to include an aggregation step which thus correlates with the polycrystalline feature of the nanoparticles obtained through this process. Moreover, the critical influence of the phosphine in this system was demonstrated a) for the outcome of the ripening mechanisms: defocusing effect and/or reshaping of the particles and b) for the surface properties: binding of the phosphine to the surface and its behavior toward oxidation was investigated by FTIR. Preliminary SQUID measurements show the impact of crystallites size on the magnetic properties.