Synthesis, self-assembly, and high performance in gas sensing of X-shaped iron oxide crystals.

X-shaped goethite iron oxide crystals were synthesized by a surfactant-free mild hydrothermal synthesis method with the aid of fluorine ions. The X-shaped goethite crystals could readily self-assemble into microscopic hollow spheres through an oil-water interface induced self-assembly method. X-shaped hematite crystals were obtained by phase topotactic transformation of the goethite precursors. The gas sensor properties of X-shaped hematite iron oxide were investigated, and the mechanism for excellent sensor properties was discussed.