Ultrafast microwave-hydrothermal synthesis of hexagonal plates of hematite

This paper reports on the synthesis of hexagonal plates of hematite, α-Fe2O3 crystals using microwave-hydrothermal (M-H) and conventional-hydrothermal (C-H) reactions. Platy α-Fe2O3 crystals which show dark red wine color were synthesized from 2M-FeCl3 and 8M-NaOH solution at both 140 and 180 °C and their morphology and crystal size were investigated. Average crystal size of hexagonal α-Fe2O3 was 0.9-1.6 μm at 140 °C and 0.8-2.1 μm at 180 °C under both M-H and C-H reactions. Compared to the formation of platy α-Fe2O3 crystals via C-H reaction, the M-H reaction led to increased rate of formation by 8 and 15 times at 140 and 180 °C, respectively. The M-H reaction yielded hexagonal plates of hematite in 2 min at 180 °C. The suspensions of platy α-Fe2O3 powders prepared at 140 and 180 °C by both C-H and M-H reactions showed dark red wine color due to similar crystal size and morphology, which have potential applications in cosmetic pigments, as anode materials in Li ion batteries.