Characterization of interfacially electronic structures of gold–magnetite heterostructures using X-ray absorption spectroscopy

Abstract

Gold-magnetite heterostructures are novel nanomaterials which can rapidly catalyze the reduction reaction of nitroaromatics. In this study, the interfacially structural and electronic properties of various morphologies of Au–Fe3O4 heterostructures were systematically investigated using X-ray absorbance spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The effect of change in electronic structure and charge transfer on electrochemically catalytic activity of Au–Fe3O4 heterostructures was further evaluated by oxygen reduction reaction (ORR). The shifts in binding energy of Au4f and Fe2p peaks in XPS spectra indicate the charge transfer between the Au and Fe3O4 nanoparticles. The increase in d-hole population of Au seeds after the conjugation with iron oxides follows the order flower-like Au–Fe3O4 (FLNPs)>dumbbell-like Au–Fe3O4 (DBNPs)>Au seeds. In addition, the Fe2+ valence state increases in Au–Fe3O4 heterostructures, which provides evidence to support the hypothesis of charge transfer between Au and Fe3O4 nanoparticles. The theoretical simulation of Au L3-edge XAS further confirms the production of Au–Fe and Au–O bonds at the interface of Au/Fe3O4 and the epitaxial linkage relationship between Au and Fe3O4 nanoparticles. In addition, the electron deficient of Au seeds increases upon increasing Fe3O4 nanoparticles on a single Au seed, and subsequently decreases the catalytic activity of Au in the Au–Fe3O4 heterostructures. The catalytic activity of Au–Fe3O4 toward ORR follows the order Au seeds>Au–Fe3O4 DBNPs>Au–Fe3O4 FLNPs, which is positively correlated to the extent of electronic deficiency of Au in Au–Fe3O4 heterostructures.