Phase-transition-induced one-dimensional amorphous α-Fe₂O₃/β-FeOOH homojunction for efficient photocatalytic water oxidation

We report a one-dimensional porous intergrowth structure consisting of amorphous α-Fe₂O₃ and akaganeite (β-FeOOH). The homojunction, which features an intimate interface as well as a clean surface, facilitates charge separation and thus improves the photocatalytic O₂ evolution activity. The success of the synthesis relies on a phase-transition process that involves the dehydration of β-FeOOH tetragonal nanorods (5.02 nm in average diameter and 25.51 nm in length, respectively). We find that the selective calcination temperature is crucial for retaining the rod shape, creating proper surface pores and intermediate phase segregations. If the temperature is too high (300°C), only crystallized α-Fe₂O₃ can be obtained. At a depressed temperature, intermediate amorphous α-Fe₂O₃, instead of the crystallized counterpart, largely emerges in situ, leading to the formation of amorphous α-Fe₂O₃/β-FeOOH intergrowth homojunctions. This preferential growth together with a type-II band alignment favors vertical interfacial charge transfer between the two components. Our results show that amorphous α-Fe₂O₃/β-FeOOH porous nanorods prepared at 200°C present a profound photocatalytic activity toward water oxidation. The rate of oxygen evolution reaches 90 μmoL h^-1 g^-1 under visible light irradiation without the addition of a cocatalyst. We believe the method can be extended for the design of other intergrowth junction structures for efficient photocatalysis.