Identification of a Fe(OH)2-like phase in the core–shell structure of nano-zero-valent Fe and its evolution when interacting with Pd2+aq ions by Mössbauer spectroscopy, XPS, and TEM

Synthesized Fe@FeOx nanoparticles (NPs) were fully characterized by spectroscopic techniques and (scanning) transmission electron microscopy to resolve the presence of a Fe(OH)2-like phase. The different phases detected in the core–shell nanostructure of these NPs were corroborated by Mössbauer and X-ray photoelectron spectroscopies. Metallic iron (Fe0), ferrous (FeII) hydroxide, magnetite (FeIII2FeIIO4), and a top layer of ferric (FeIII) oxide were identified. Interestingly, ferrous hydroxide reacted with Pd2+aq upon coating of the supporting core–shell material when Pd was added to produce Fe@FeOx/Pd NPs.