Synthesis of discrete and dispersible MoS2 nanocrystals

MoS2 nanoparticles of size <5 nm have been synthesized via the reaction of Mo(CO)6 with elemental sulfur in trioctylphosphine oxide and 1-octadecene at temperatures from 270 to 330 degrees C. The MoS2 nanoparticles are discrete and dispersible in a variety of nonpolar organic solvents, including toluene, chloroform, and pyridine. The size of the particles can be effectively tuned by varying the temperature, yielding nearly monodisperse samples (<10% standard deviation) as evidenced by transmission electron microscopy (TEM). Additionally, larger (20-50 nm) onion- and tube-shaped MoS2 nanoparticles can be obtained by decreasing the amount of the coordinating solvent (trioctylphosphine oxide) relative to 1-octadecene. As-prepared samples are poorly crystalline, showing only weak contrast in the TEM and an absence of the first-order (00 l) reflection in powder X-ray diffraction that is indicative of regular MoS2 stacking. Samples heated in situ in the TEM are observed to develop contrast and lattice fringes as the temperature is raised to 550 degrees C. Ex-situ heated samples show the appearance of the first order (00l) reflection at temperatures >870 degrees C.