Phase Pure Pyrite FeS2 Nanocubes Synthesized Using Oleylamine as Ligand, Solvent, and Reductant

Pyrite (FeS2) nanocrystals with a narrow size distribution and optical absorption from 1600 to 380 nm, were synthesized in a Single stage by reacting ferrous chloride with elemental sulfur in oleylamine (OAm) without an additional ligand. X-ray,diffraction, Raman, and scanning electron microscopy showed' that pyrite cubes with dimensions of 88 14 nm formed at 200 degrees C, an S to Fe ratio of 6, and 1 h reaction time in OAm. The time required to form phase pure pyrite depended On the S to Fe ratio. has purity was obtained in less than 1 hat a ratio of 6, but times as long as 24 h were necessary at a ratio of 2.75. The rate of pyrite formation increased with higher sulfur concentrations, which shows that molecules containing sulfur are involved in the rate-determining step. Both H2S and polysulfides of the form S-n(2-) are known to form in oleylamine. The slow step is the reaction between FeS and these molecules. Fe2+S2- undergoes nucleophilic attack by H2S and S-n(2-); S2- converts to S- and sulfur is transferred forming pyrite Fe2+S22-.