Synthesis, characterization and assembly of metal pnictide nanoparticles, and evaluation of their physicochemical (catalytic, magnetic, and semiconducting) properties

Synthesis of transition metal phosphide (Ni2P) and arsenide (MnAs) discrete nanoparticles was conducted by following a solution-phase arrested precipitation route and the size- and structure-dependent physicochemical properties of these materials were explored. Furthermore, the assembly of metal phosphide nanoparticles into a network structure via a sol-gel process and the evaluation of their structure related properties also was conducted.;The surface ligation chemistry of unsupported Ni2P nanoparticles prepared by arrested precipitation was found to strongly impact the structural integrity and the hydrodesulfurization (HDS) catalytic activity of Ni 2P nanoparticles. The HDS activity of unsupported surface modified Ni2P nanoparticles is higher than that of unsupported Ni2P prepared by temperature programmed reduction (TPR) but considerably lower than silica-supported Ni2P prepared by TPR. However, by supporting the pre-formed Ni 2P nanoparticles on silica, activity comparable to that of silica-supported Ni2P prepared by TPR can be achieved. The synthetic control offered by the Ni2P nanoparticle preparation, not achieved by TPR methods, is expected to enable a systematic study of particle size and shape effects on HDS activity.;By using arrested precipitation reactions, for the first time, discrete and dispersible MnAs nanoparticles have been prepared and their magnetic properties evaluated. Syntheses were developed to target both the thermodynamically stable alpha-type (hexagonal) and the metastable beta-type (orthorhombic) MnAs nanoparticles. Surprisingly, both types of ∼25 nm particles exhibit nearly identical ferromagnetic behavior with blocking temperatures, T B, in the region ∼275-310 K, TC's of 315 K and room temperature coercivities of HC ∼ 190-320 Oe. No evidence of the expected structural transition from alpha to beta-MnAs at TC is observed.;Oxidative sol-gel assembly of nanoparticles to make nanoparticulate gels was successfully employed to Ni2P nanoparticles, and further extended to MnP and InP nanoparticles, for the first time. The gels were transformed into highly porous, high surface area (175-270 m2/g) 3-D structures (aerogels) via CO2 supercritical drying. Relative to discrete nanoparticles, Ni2P aerogels are less active to HDS, MnP aerogels have similar magnetic properties, and InP aerogels exhibit a greater degree of quantum confinement.