Template-Free Hydrothermal Synthesis and Formation Mechanism of Hematite Microrings

Hematite microrings with an outer diameter similar to 12 mu m, inner diameter similar to 4 mu m, and thickness similar to 500 nm have been successfully synthesized by a facile template-free hydrothermal method using K3Fe(CN)(6) and NaOH as reagents through a redox reaction. The influence of the reaction time, reaction temperature, concentration of K3Fe(CN)(6), and NaOH on the evolution of shape and structures has been studied in detail. The optimal condition for preparation of the microrings is 180 degrees C for 5 h, the NaOH concentration is 4 M, and the K3Fe(CN)(6) concentration is 0.02 M. The possible hollowing growth mechanism for the hematite microrings has been discussed. Magnetic hysteresis measurement revealed that hematite microrings after calcination at 700 degrees C for 4 h display a magnetic behavior with remanent magnetization of 0.211 emu/g and coercivity of 2005 Oe at room temperature.