Controlling the sulfidation process of iron nanoparticles: accessing iron-iron sulfide core-shell structures

Iron sulfide nanocomposites have been prepared through reactions of bis[bis(trimethylsilyl)amido]iron(II) or zerovalent iron nanoparticles (NPs) with hydrogen sulfide gas. The chemical composition of these materials was analyzed by TEM, XRD, WAXS and Mössbauer measurements. Decomposition of bis[bis(trimethylsilyl)amido]iron(II) under an H2S atmosphere in the presence of palmitic acid produces thin iron sulfide nanoflakes, which seemingly consist of Fe2S2 and Fe7S8. The sulfidation of 9 nm zerovalent iron NPs with H2S yields thin nano flakes exhibiting the same iron sulfide phases and residual iron. Remarkably, treatment of slightly larger iron NPs (13 nm) with H2S (or alternatively benzylthiol) yields well-shaped iron-iron sulfide core-shell particles. These particles exhibit a crystalline iron core and an amorphous iron sulfide shell, which likely consists of Fe2S2, Fe7S8 and Fe1-XS. Magnetic measurements on these core-shell particles show a decrease of the total magnetization (compared to bulk iron) coming along with the sulfidation process. Owing to the partially preserved ferromagnetic character these iron-iron sulfide core-shell particles were found to have magnetic heating properties.