Low-Field Magnetic Separation of Monodisperse Fe 3 O 4 Nanocrystals

Abstract

Magnetic separations at very low magnetic field gradients (3O₄) nanocrystals (NCs) were shown to respond to low fields in a size-dependent fashion. The particles apparently do not act independently in the separation but rather reversibly aggregate through the resulting high-field gradients present at their surfaces. Using the high specific surface area of Fe₃O₄ NCs that were 12 nanometers in diameter, we reduced the mass of waste associated with arsenic removal from water by orders of magnitude. Additionally, the size dependence of magnetic separation permitted mixtures of 4- and 12-nanometer–sized Fe₃O₄ NCs to be separated by the application of different magnetic fields.