摘要
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-Fe <sub>3</sub> O <sub>4</sub> 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-Fe <sub>3</sub> O <sub>4</sub> 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 Fe <sub>3</sub> O <sub>4</sub> nanoparticles. The increase in d-hole population of Au seeds after the conjugation with iron oxides follows the order flower-like Au-Fe <sub>3</sub> O <sub>4</sub> (FLNPs)>dumbbell-like Au-Fe <sub>3</sub> O <sub>4</sub> (DBNPs)>Au seeds. In addition, the Fe <sup>2+</sup> valence state increases in Au-Fe <sub>3</sub> O <sub>4</sub> heterostructures, which provides evidence to support the hypothesis of charge transfer between Au and Fe <sub>3</sub> O <sub>4</sub> nanoparticles. The theoretical simulation of Au L <sub>3</sub> -edge XAS further confirms the production of Au-Fe and Au-O bonds at the interface of Au/Fe <sub>3</sub> O <sub>4</sub> and the epitaxial linkage relationship between Au and Fe <sub>3</sub> O <sub>4</sub> nanoparticles. In addition, the electron deficient of Au seeds increases upon increasing Fe <sub>3</sub> O <sub>4</sub> nanoparticles on a single Au seed, and subsequently decreases the catalytic activity of Au in the Au-Fe <sub>3</sub> O <sub>4</sub> heterostructures. The catalytic activity of Au-Fe <sub>3</sub> O <sub>4</sub> toward ORR follows the order Au seeds>Au-Fe <sub>3</sub> O <sub>4</sub> DBNPs>Au-Fe <sub>3</sub> O <sub>4</sub> FLNPs, which is positively correlated to the extent of electronic deficiency of Au in Au-Fe <sub>3</sub> O <sub>4</sub> heterostructures. © 2013 Elsevier Inc.