Effects of morphology and exposed facets of α-Fe₂O₃ nanocrystals on photocatalytic water oxidation

Shape and facet engineering of crystals at the nanoscale level has become an important strategy for optimizing the reactivity of catalysts in heterogeneous catalysis. We report here the fabrication of four morphology-controlled α-Fe₂O₃ catalysts with exposed specific facets by a solvothermal method. The effects of morphology and exposed facets of these α-Fe₂O₃ nanocrystals towards visible light-driven water oxidation have been investigated. Water oxidation was carried out using two catalytic systems, Fe₂O₃/[Ru(bpy)₃]²⁺/S₂O₈^2- and Fe₂O₃/AgNO₃, at λ > 420 nm. The α-Fe₂O₃ nanocubes with exposed {012} facets exhibit much higher catalytic activity than α-Fe₂O₃ nanoflakes with {001} facets. This work demonstrates that the catalytic activity of α-Fe₂O₃ nanocrystals in photocatalytic water oxidation is morphology-dependent and the reactivity trend can be rationalized in terms of exposed facets in the order of {012} > {001}. This study provides a new approach to the design of highly effective water oxidation catalysts by engineering the morphology and the exposed facets of crystals.