Hexagonal bi-pyramid α-Fe2O3 microcrystals: Unusual formation, characterization and application for gas sensing

•Hexagonal bi-pyramid α-Fe2O3 microcrystals have been facilely fabricated by a two-step hydrothermal method.•HB-α-Fe2O3 MCs has a large specific surface area.•HB-α-Fe2O3 MCs presents high gas sensing properties and stable stability. A hydrothermal strategy is developed to realize the controllable synthesis of hexagonal bipyramid α-Fe2O3 microcrystals (HB-α-Fe2O3 MCs) using FeOOH nanorods as precursor. Based on the SEM, TEM and BET analysis, such HB-α-Fe2O3 MCs have a perfect hexagonal bi-pyramid structure with the specific surface area of 78.2 m2 g–1. Formation mechanism of HB-α-Fe2O3 MCs is tentatively proposed by comparative structure-evolution investigations. By virtue of their structural advantages, HB-α-Fe2O3 MCs served as a gas sensor exhibit remarkable sensor response, selectivity, and response/recovery towards ethanol gas. All these impressive performances indicate their appealing application in advanced gas sensors. This well-controllable hexagonal bipyramid microcrystals are opening up an unusual way to fabricate advanced electrodes for sensor, catalyst, and energy-related applications.