No abstract

Ammonium sulfide ((NH4)2S) exhibits high reactivity as a sulfide reagent in anion exchange reactions that transform CoO to cobalt sulfide nanoparticles (NPs). The faster diffusion of Co(2+) and O(2-) than the incoming S(2-) during the anion exchange causes a significant expansion of the NP voids. The low temperature (70 °C) anion exchange reaction produces amorphous cobalt sulfide NPs with Co : S ratio of ca. 3 : 4, which are converted into crystalline NPs with a major phase of cubic Co3S4 by annealing at high temperature in an organic solution.

The layer-by-layer processing of Au/Au(x)Pd(1-x) core/alloy nanoparticles via microwave irradiation (MWI) based hydrothermal heating is described. Alloy shell growth was monitored by the attenuation of surface plasmon resonance (SPR) as a function of shell thickness and composition. Discrete dipole approximation (DDA) correlated the SPR to particle morphology.

The alloy phase behavior of nanoparticle (NP) interfaces has been used to tailor asymmetric growth. Using either Au-Pd core-shell or Au-Au(x)Pd(1-x) core-alloy NP starting materials, the deposition of Ag resulted in asymmetric and symmetric growth respectively. The phase segregation of the interface was confirmed by TEM and electrocatalytic activity.