Spatial and Temporal Confinement of Salt Fluxes for the Shape-Controlled Synthesis of Fe2O3 Nanocrystals

Here, molten salt syntheses (MSS) are coupled with ultrasonic spray pyrolysis to yield single-crystalline Fe2O3 nano- and microparticles with controlled shapes and phases. It was previously demonstrated that aerosol-assisted MSS can produce single-crystalline nanoplates. Now, by selecting different molten salt flux components, various crystalline phases and particle shapes are accessed via the dissolution of Fe2O3 colloids, followed by precipitation of the iron oxide products from molten alkali carbonates that are spatially and temporally confined in the aerosol phase. This confinement limits crystal growth to the nanoscale and provides access to products at different stages of supersaturation. The resulting powders consist of hexagonal nanoplates (α- or γ-Fe2O3), rhombohedra (α-Fe2O3), or octahedra (LiFe5O8) depending on the selected molten salt flux. Significantly, this synthetic approach represents a continuous and potentially general route to the generation of shape- and phase-controlled nano- and microcrystals given the diversity of materials previously prepared by molten salt techniques.