Synthesis of 2D Hexagonal Hematite Nanosheets and the Crystal Growth Mechanism

Nanostructure engineering of hematite is a promising strategy to overcome its performance limitations as a photodegradation catalyst for organic dyes or toxic organic chemicals. Precise control of exposed facets plays a vital role as an optimization strategy. Although great progress has been made in the synthesis of different crystal morphologies, design principles remain ad hoc, awaiting systematic control of facet expression within a clean synthesis protocol yielding versatile results. Herein, we report a simple method that enables precise morphology control to synthesize 2D hexagonal hematite nanosheets from two-line ferrihydrite. Nanosheet sizes and facet proportions were successfully tuned by changing the pH, the ratio of solvent ethanol to water, and the concentration of Fe^III ions. The growth mechanism appears to involve a combination of ferrihydrite solid-state transformation and assembly into hematite, followed by an ion-by-ion growth that perfects the surface terminations. The finding helps to establish a rational basis for the design and optimization of hematite nanostructures.