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

Abstract

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 °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. Phase purity was obtained in less than 1 h at 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 Sn2– 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 Sn2–; S2– converts to S– and sulfur is transferred ...