Reactions of Nanoscale Zero-Valent Iron with Ni(II): Three-Dimensional Tomography of the “Hollow Out” Effect in a Single Nanoparticle

Three-dimensional tomography of reactions of Ni(II) with a single zero-valent iron nanoparticle (∼60 nm) is achieved with spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) integrated with energy-dispersive X-ray spectrometry (EDS). High-resolution two- and three-dimensional images provide proof of the hollow-out effect of the zero-valent iron nanoparticle; i.e., the redox reactions attack and dissolve the core of a nanoparticle and form a hollow doughnutlike structure. Results offer evidence of the unique characteristics and catalytic functions of zero-valent iron nanoparticles for the treatment of heavy metal ions such as Ni(II) and provide direct confirmation of the core–shell structure. Furthermore, results demonstrate the potential of STEM–EDS for visualizing the complex morphology and elemental composition of nanomaterials and mapping reactions of environmental pollutants in a single nanoparticle at near-atomic (∼0.1 nm) resolution.