Simultaneous Control of Composition, Size, and Morphology in Discrete Ni2-xCoxP Nanoparticles

A synthetic protocol developed to produce phase-pure, nearly monodisperse Ni2-xCoxP nanoparticles (x <= 1.7) is described. The Ni2-xCoxP particles vary in size, ranging from 914 nm with standard deviations of <20% (based on transmission electron microscopy analysis), and the actual metal ratios obtained from energy-dispersive spectroscopy closely follow the targeted ratios. With increasing Co, samples with larger size distributions are obtained and include particles with voids, attributed to the Kirkendall effect. To probe the mechanism of ternary phosphide particle formation, detailed studies were conducted for Ni:Co = 1:1 as a representative composition. It was revealed that the P:M ratio, heating temperature, and heating time have a large impact on the nature of both intermediate and final crystalline particles formed. By tuning these conditions, nanoparticles can be produced with different sizes (from ca. 7-25 nm) and morphologies (hollow versus dense).