Microwave Synthesis of Cu, Ni, and Cu/Ni Core/Shell Nanoparticles From Triethylene Glycol Solutions of Metal Acetates*

Elemental Cu, elemental Ni, and bimetallic Cu core/Ni shell nanoparticles have been prepared from triethylene glycol solutions of metal acetates in a microwave reactor. Unlike thermal heating, microwave heating allows more rapid heating profiles and, therefore, can more efficiently isolate intermediate reaction products. For example, very small phase pure Cu₂O nanoparticles are initially obtained at reaction temperatures from 200-225 °C which, after 5-10 minutes, rapidly decompose to larger elemental Cu nanoparticles. In comparison, elemental FCC Ni is the initial reaction product at 250 °C with a slow subsequent conversion to HCP Ni (or, perhaps, a hexagonal nickel carbide) at longer reaction times. The relatively clean separation between the temperatures at which Cu and Ni nanoparticles form makes it possible to prepare Cu core/Ni shell nanoparticles from mixed Cu and Ni acetate solutions first heated to 225 °C for a period of 5-10 minutes followed by an additional 5 minute reaction time at 250 °C.