Bottom-Up Assembly of Ni₂P Nanoparticles into Three-Dimensional Architectures: An Alternative Mechanism for Phosphide Gelation

The synthesis of Ni₂P nanoparticle three-dimensional architectures using two different approaches is reported. The oxidation-induced sol–gel method involves chemical oxidation of surface phosphorus to form P–O–P linkages between particles in the gel network, similar to the mechanism originally reported for InP nanoparticles. The second method, metal-assisted gelation, occurs by cross-linking of pendant carboxylate functionalities on surface-bound thiolate ligands via metal ions to yield an interconnected particle network. The method of gel network formation can be tuned by changing the surface ligand terminal functionalities and the nature (oxygen-transferring or non-oxygen-transferring) of the oxidant. Both methods produce porous, high surface area materials with thermal stabilities above 400 °C

Synthesis and Characterization of Discrete Fe_<i>x</i>Ni_2–<i>x</i>P Nanocrystals (0 < <i>x</i> < 2): Compositional Effects on Magnetic Properties

Ternary Fe_<i>x</i>Ni_2–<i>x</i>P (0 < <i>x</i> < 2) phases exhibit a range of useful properties that can be augmented or tuned by confinement to the nanoscale including hydrotreating catalytic activity for small <i>x</i> and near-room temperature ferromagnetism for high <i>x</i>. In this work, a solution-phase arrested-precipitation method was developed for the synthesis of Fe_<i>x</i>Ni_2–<i>x</i>P over all values of <i>x</i> (0 < <i>x</i> < 2). The synthesis involves preparation of Ni–P amorphous particles, introduction of the Fe precursor to form amorphous Fe–Ni–P particles, and high-temperature conversion of Fe–Ni–P particles into crystalline ternary phosphide nanocrystals. The ternary Fe_<i>x</i>Ni_2–<i>x</i>P nanocrystals crystallize in the hexagonal Fe₂P-type structure, and the morphology of the nanocrystals showed a distinct compositional dependence, transitioning from about 11 nm diameter spheres to rods with aspect ratios approaching 2 as the Fe fraction is increased (<i>x</i> ≥ 1.2). Lattice parameters do not follow Vegard’s law, consistent with Mössbauer data showing preferential site occupation by Fe of the tetrahedral over the square pyramidal sites at low Fe concentrations, and the opposite effect for <i>x</i> > 0.8. Magnetic measurements of Fe_<i>x</i>Ni_2–<i>x</i>P (<i>x</i> = 1.8, 1.4, and 1.2) nanorods showed a strong compositional dependence of the Curie temperature (<i>T</i>_C) that differs from observations in bulk phases, with the highest <i>T</i>_C (265 K) obtained for <i>x</i> = 1.4