A valve-assisted snapshot approach to understand the hydrothermal synthesis of α-Fe2O3 nanorods

A novel valve-assisted pressure autoclave is described, facilitating ‘snapshot’ investigations of hydrothermal synthesis (HS) product suspensions rapidly quenched in liquid nitrogen. The approach gives near in situ descriptions of the HS reaction products, as characterised using transmission electron microscopy, and provides fundamental insight into the mechanisms of crystal growth. An investigation into the development of α-Fe2O3 nanorods from aqueous FeCl3 solution clarifies the role of intermediate β-FeOOH nanorod and α-Fe2O3 nanoparticle phases during α-Fe2O3 nanorod growth. It is shown that intermediate β-FeOOH precipitation and dissolution occurs alongside the anisotropic growth of α-Fe2O3 nanorods through the coalescence of primary α-Fe2O3 nanoparticles. It is considered that this valve-assisted technique will be widely applicable to the study of many other HS systems