Self-assembled monolayer coatings on amorphous iron and iron oxide nanoparticles: Thermal stability and chemical reactivity studies

Self-assembled coatings of long chain thiols on nanoparticles of amorphous iron as well as on amorphous Fe₂O₃ were formed. The thermal stability of these coatings was investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the particles and by mass spectrometric analysis of the molecules desorbed from the surface by heating the amorphous substrates. The results showed a sharp weight loss centered at about 200 °C for the thiol-coated particles. The mass spectrometric study of the molecules removed from the surface of the amorphous iron revealed the formation of a dialkyl thioether. For the amorphous Fe₂O₃ surfaces, a dialkyl disulfide was removed from the surface. The desorptions from the Fe₂O₃ surface occurred at higher temperatures than those for the amorphous iron. The different mechanisms responsible for these desorption reactions are discussed.