Microstructural evolution of iron oxide hollow nanoparticles toward iron oxide nanotubes in a prolonged sintering condition

Prolonged sintering of iron oxide hollow nanoparticles (HNPs) during chemical vapor condensation (CVC) at 800 °C for 6 h showed some interesting morphologies of the iron oxide nanotubes. TEM and XRD studies confirmed that single-walled nanotubes of a mixed phase of α, β, and γ-Fe₂O₃, with a wall thickness of less than 10 nm and an outer diameter of approximately 50 nm were synthesized. The formation of iron oxide nanotubes was thought to be an evolution of iron oxide HNPs based on the sintering.