Investigations on Iron Sulfide Nanosheets Prepared via a Single-Source Precursor Approach

Two-dimensional (2D) magnetic pyrrhotite (Fe 7 S 8 ) and greigite (Fe 3 S 4 ) nanosheets were synthesized by pyrolyzing, respectively, single-source precursors such as Fe(Ddtc) 2 (Phen) (Phen = 1,10-phenanthroline; Ddtc = diethyldithiocarbamate) and Fe(Ddtc) 3 in oleylamine. Under optimized reaction temperature of 280 °C, both monoclinic Fe 7 S 8 and cubic Fe 3 S 4 obtained presented hexagonal sheet structure with sizes of 500–800 nm and 100–500 nm, respectively. AFM measurements revealed that both of these two types of nanosheets had a nearly identical thickness of 50 nm. Further XRD measurements revealed that the reaction temperature played a critical role in determining the crystalline structure as well as the chemical composition of the resultant nanosheets. In the reaction temperature range of 240−320 °C, a higher reaction temperature generally favored the transformations of monoclinic Fe 7 S 8 to hexagonal FeS, and cubic Fe 3 S 4 to hexagonal Fe 7 S 8, respectively. The magnetic properties of the resultant nanosheets were accordingly altered against the reaction temperature. Further experimental results obtained by combining different types of solvents suggested that oleylamine was necessary for the formation of hexagonal Fe 7 S 8 nanosheets. In contrast, it only helped prevent the hexagonal Fe 3 S 4 nanosheets from agglomeration. It was also found that both pyrrhotite (Fe 7 S 8 ) and greigite (Fe 3 S 4 ) nanosheets were metastable under ambient conditions. Systematic XPS measurements were carried out to investigate the air stabilities of the resultant nanosheets.