BiFeO₃/α-Fe₂O₃ core/shell composite particles for fast and selective removal of methyl orange dye in water.

BiFeO3/α-Fe2O3 core/shell composite particles featuring fast removal, selective adsorption, and magnetic recycle capability on anionic methyl orange (MO) dye in water was synthesized by a two-step chemical route. A discontinuous and rough shell consisting of the α-Fe2O3 nanoparticles was deposited on the BiFeO3 core surface preferentially, forming raspberry-like core/shell particle morphology. The core/shell particles demonstrated a pronounced adsorption to the MO molecules when compared with particulate mixtures of the same molar ratio. At an initial MO concentration of 2.5×10(-5) M, nearly 80% of the dye molecules were captured by the core/shell particles within 5 min at an acidic pH of 5.2. Desorption of the MO dye could be made easily when the solution pH was adjusted to 9.5. This together with a minute adsorption capacity (<2%) from solutions consisting of cationic methylene blue (MB) dye suggests that the adsorption selectivity was in part due to electrostatic interactions between the dye molecules and the core/shell particles.