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

•Magnetic BiFeO3/α-Fe2O3 core/shell particles show fast removal of MO dye in water.•Adsorption of MO dye occurs at acidic pH, while desorption takes place at basic pH.•Adsorption selectivity is demonstrated when cationic MB dye was used.

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.

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