Oxidation Conversion of Carbon-Encapsulated Metal Nanoparticles to Hollow Nanoparticles

Abstract

We synthesized R-Fe 2 O 3 hollow nanoparticles by directly oxidizing the carbon-encapsulated iron carbide (Fe 3 C@C) nanoparticles in air. In this paper, the conversion mechanism of Fe 3 C@C to hollow nanoparticles was deduced in detail by comparatively investigating the morphologies and compositions of the oxidized products at different oxidation stages using transmission electron microscope (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that both oxygen and carbon play important roles in the formation of hollow nanostructures, wherein oxygen is the driving force for the outward diffusion of core species and the carbon shell not only provides the diffusion vacancies but also effectively moderates the interdiffusion rates of metal core materials and oxygen. A growth model was proposed: during the oxidation process, three diffusion processes occur including the inward diffusion of oxygen along the carbon shell, outward diffusion of core materials, and inward diffusion of vacancies from carbon shell to core. The outward diffusion of core species involves two steps: the first step is the diffusion of Fe 3 C from core to carbon shells, which is only a physical change (single-crystal Fe 3 C was changed to multicrystal Fe 3 C); and the second one is the diffusion and chemical reactions of Fe 3 C in carbon shells with oxygen (the multicrystal Fe 3 C was oxidized to Fe 3 O 4 and then to R-Fe 2 O 3 ). The two-step diffusion is a theoretical extension to the nanoscale Kirkendall effect, which is expected to be valid in other diffusion couples and theoretical simulation.

Iron-Doped Molybdenum Carbide Catalyst with High Activity and Stability for the Hydrogen Evolution Reaction

“…97 The binding energy of Fe 2p 3/2 electron in Fe doped β-Mo 2 C is comparable to that in Fe 3 C (~707.50 eV) and Fe 5 C 2 (~707.00 eV). [98][99][100] Unexpected and important information has been collected from valence bands (VB) studies on Fe doped β-Mo 2 C materials as seen in Fig. 5.…”

A microfibre assembly of an iron-carbon composite with giant magnetisation

“…Because the iron carbide sphere surfaces were covered with amorphous carbon, we employed 3-kV Ar ion bombardment to remove the surface layer to a depth of 50 nm. For the Fe 2p region, the two peaks at 707.45 and 720.28 eV suggested the presence of iron carbide components2021. The C1s spectrum was fitted with three components.…”

A General Strategy for the Preparation of Hollow Carbon Nanocages by NH4Cl‐Assisted Low‐Temperature Heat Treatment

“…The outward diffusion of Fe may be the main type of diffusion during the removal of iron particles and this was also observed by other researchers. [32] To promote the outward diffusion of iron nanoparticles, there must be a driving force; one suggestion was particle melting. [33] It has been reported that iron nanoparticles become unstable when heated even at 250 8C.…”